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 $67.78   12.271%   $76.0973   $76.10   $76.10   $76.10  
  Purchase #2 $48.55   13.133%   $54.9261   $54.93   $54.95   $54.90  
  Purchase #3 $51.89   13.266%   $58.7737   $58.77   $58.75   $58.80  
  Purchase #4 $181.56   12.199%   $203.7085   $203.71   $203.70   $203.70  
  Purchase #5 $236.81   4.412%   $247.2581   $247.26   $247.25   $247.30  
  Purchase #6 $53.58   10.802%   $59.3677   $59.37   $59.35   $59.40  
  Purchase #7 $156.96   8.214%   $169.8527   $169.85   $169.85   $169.90  
  7 purchase totals = $797.13       $869.9841   $869.99   $869.95   $870.10