Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $109.32   9.176%   $119.3512   $119.35   $119.35   $119.40  
  Purchase #2 $116.82   9.674%   $128.1212   $128.12   $128.10   $128.10  
  Purchase #3 $7.71   5.318%   $8.12   $8.12   $8.10   $8.10  
  Purchase #4 $97.87   4.531%   $102.3045   $102.30   $102.30   $102.30  
  Purchase #5 $158.49   7.554%   $170.4623   $170.46   $170.45   $170.50  
  Purchase #6 $117.97   4.240%   $122.9719   $122.97   $122.95   $123.00  
  Purchase #7 $222.93   7.735%   $240.1736   $240.17   $240.15   $240.20  
  7 purchase totals = $831.11       $891.5047   $891.49   $891.40   $891.60