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 $29.26   13.801%   $33.2982   $33.30   $33.30   $33.30  
  Purchase #2 $90.78   13.242%   $102.8011   $102.80   $102.80   $102.80  
  Purchase #3 $99.39   4.428%   $103.791   $103.79   $103.80   $103.80  
  Purchase #4 $173.39   9.246%   $189.4216   $189.42   $189.40   $189.40  
  Purchase #5 $81.97   13.228%   $92.813   $92.81   $92.80   $92.80  
  Purchase #6 $44.69   3.174%   $46.1085   $46.11   $46.10   $46.10  
  Purchase #7 $170.95   13.827%   $194.5873   $194.59   $194.60   $194.60  
  7 purchase totals = $690.43       $762.8207   $762.82   $762.80   $762.80