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 $48.56   12.713%   $54.7334   $54.73   $54.75   $54.70  
  Purchase #2 $158.79   10.801%   $175.9409   $175.94   $175.95   $175.90  
  Purchase #3 $190.92   11.816%   $213.4791   $213.48   $213.50   $213.50  
  Purchase #4 $24.40   7.278%   $26.1758   $26.18   $26.20   $26.20  
  Purchase #5 $120.96   9.761%   $132.7669   $132.77   $132.75   $132.80  
  Purchase #6 $222.46   3.559%   $230.3774   $230.38   $230.40   $230.40  
  Purchase #7 $28.42   10.583%   $31.4277   $31.43   $31.45   $31.40  
  7 purchase totals = $794.51       $864.9012   $864.91   $865.00   $864.90