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 $62.98   13.734%   $71.6297   $71.63   $71.65   $71.60  
  Purchase #2 $195.93   7.569%   $210.7599   $210.76   $210.75   $210.80  
  Purchase #3 $31.79   8.627%   $34.5325   $34.53   $34.55   $34.50  
  Purchase #4 $59.38   6.667%   $63.3389   $63.34   $63.35   $63.30  
  Purchase #5 $150.30   4.518%   $157.0906   $157.09   $157.10   $157.10  
  Purchase #6 $124.31   12.109%   $139.3627   $139.36   $139.35   $139.40  
  Purchase #7 $209.45   12.858%   $236.3811   $236.38   $236.40   $236.40  
  7 purchase totals = $834.14       $913.0954   $913.09   $913.15   $913.10