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 $151.64   5.344%   $159.7436   $159.74   $159.75   $159.70  
  Purchase #2 $68.50   3.613%   $70.9749   $70.97   $70.95   $71.00  
  Purchase #3 $250.38   12.584%   $281.8878   $281.89   $281.90   $281.90  
  Purchase #4 $199.29   5.352%   $209.956   $209.96   $209.95   $210.00  
  Purchase #5 $25.86   10.349%   $28.5363   $28.54   $28.55   $28.50  
  Purchase #6 $232.28   12.432%   $261.157   $261.16   $261.15   $261.20  
  Purchase #7 $30.88   4.425%   $32.2464   $32.25   $32.25   $32.20  
  7 purchase totals = $958.83       $1,044.5020   $1,044.51   $1,044.50   $1,044.50