Use normal  rounding rules to round up or down. Doing this will make it easier to calculate the percent discount of the number. For example, if the original price of a shirt is $47.89, round the price up to $50.00 To mentally calculate 10% of a price, think of the price written as dollars and cents with a decimal point. Then, move the decimal point one place to the left. This will show you the number that is equal to 10%. For example, to calculate 10% of $50, think $50=$50.00=$5.00{\displaystyle \$50=\$50.00=\$5.00}. So, 5 is 10% of 50. To figure out the number of tens, divide by the percentage by 10 using normal division rules. Don’t worry about fives in the percentage for now. For example, if a shirt is 35% off, you would need to know how many tens are in 35. Since 35÷10=3.5{\displaystyle 35\div 10=3.5}, there are 3 tens in 35. The factor is determined by the number of tens in the percent off. Since you determined what 10% of the price is, find a larger percent by multiplying by the number of tens. For example, if you found that 10% of $50 is 5, to find out how much 30% of 50 is, you would multiply $5 by 3, since there are 3 tens in 30: 5×3=15{\displaystyle 5\times 3=15}. So, 30% of $50 is $15. You will need to do this step if the percent off discount ends in a 5 rather than a 0 (for example, 35% or 55% off). It is easy to calculate 5% by simply dividing 10% of the original price by 2, since 5% is half of 10%. For example, if 10% of $50 is $5, then 5% of $50 is $2.50, since $2.50 is half of $5. This will give you the total estimated discount of the item. For example, if a shirt is 35% off, you first found 30% of the original price was $15. Then you found that 5% of the original price was $2.50. So adding the values of 30% and 5%, you get $15+$2.50=$17.50{\displaystyle \$15+\$2.50=\$17.50}. So, the estimated discount of the shirt is $17.50. This will give you an estimate of the sale price of the item. For example, if the rounded price of a shirt is $50, and you found the 35% discount to be $17.50, you would...

===
Write a summary of the previous text in Vietnamese:
Làm tròn giá bán ban đầu về số tròn chục gần nhất. Tính 10 phần trăm của giá đã làm tròn. Xác định số đơn vị chục trong phần trăm giảm giá. Nhân 10% giá đã làm tròn với số nhân. Tính mức 5% của giá làm tròn nếu cần. Thêm phần 5% vào giá trị chiết khấu nếu cần. Lấy giá đã làm tròn trừ đi giá trị chiết khấu.