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 $92.28   3.764%   $95.7534   $95.75   $95.75   $95.80  
  Purchase #2 $230.38   13.697%   $261.9351   $261.94   $261.95   $261.90  
  Purchase #3 $87.61   11.109%   $97.3426   $97.34   $97.35   $97.30  
  Purchase #4 $118.92   13.339%   $134.7827   $134.78   $134.80   $134.80  
  Purchase #5 $51.59   13.163%   $58.3808   $58.38   $58.40   $58.40  
  Purchase #6 $159.46   6.438%   $169.726   $169.73   $169.75   $169.70  
  Purchase #7 $63.68   11.645%   $71.0955   $71.10   $71.10   $71.10  
  7 purchase totals = $803.92       $889.0161   $889.02   $889.10   $889.00