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 $76.28   13.713%   $86.7403   $86.74   $86.75   $86.70  
  Purchase #2 $67.89   12.312%   $76.2486   $76.25   $76.25   $76.20  
  Purchase #3 $182.69   10.669%   $202.1812   $202.18   $202.20   $202.20  
  Purchase #4 $247.72   5.273%   $260.7823   $260.78   $260.80   $260.80  
  Purchase #5 $214.66   10.381%   $236.9439   $236.94   $236.95   $236.90  
  Purchase #6 $9.50   13.525%   $10.7849   $10.78   $10.80   $10.80  
  Purchase #7 $58.45   11.501%   $65.1723   $65.17   $65.15   $65.20  
  7 purchase totals = $857.19       $938.8535   $938.84   $938.90   $938.80