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 $204.62   9.610%   $224.284   $224.28   $224.30   $224.30  
  Purchase #2 $42.29   11.345%   $47.0878   $47.09   $47.10   $47.10  
  Purchase #3 $71.48   4.865%   $74.9575   $74.96   $74.95   $75.00  
  Purchase #4 $141.26   8.601%   $153.4098   $153.41   $153.40   $153.40  
  Purchase #5 $149.54   11.768%   $167.1379   $167.14   $167.15   $167.10  
  Purchase #6 $247.30   5.428%   $260.7234   $260.72   $260.70   $260.70  
  Purchase #7 $94.63   6.849%   $101.1112   $101.11   $101.10   $101.10  
  7 purchase totals = $951.12       $1,028.7116   $1,028.71   $1,028.70   $1,028.70