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 $78.28   13.299%   $88.6905   $88.69   $88.70   $88.70  
  Purchase #2 $78.53   5.709%   $83.0133   $83.01   $83.00   $83.00  
  Purchase #3 $119.71   11.554%   $133.5413   $133.54   $133.55   $133.50  
  Purchase #4 $205.78   10.783%   $227.9693   $227.97   $227.95   $228.00  
  Purchase #5 $232.45   6.587%   $247.7615   $247.76   $247.75   $247.80  
  Purchase #6 $195.50   11.517%   $218.0157   $218.02   $218.00   $218.00  
  Purchase #7 $152.46   11.186%   $169.5142   $169.51   $169.50   $169.50  
  7 purchase totals = $1,062.71       $1,168.5058   $1,168.50   $1,168.45   $1,168.50