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 $215.86   13.759%   $245.5602   $245.56   $245.55   $245.60  
  Purchase #2 $231.78   9.689%   $254.2372   $254.24   $254.25   $254.20  
  Purchase #3 $81.39   5.733%   $86.0561   $86.06   $86.05   $86.10  
  Purchase #4 $61.92   12.634%   $69.743   $69.74   $69.75   $69.70  
  Purchase #5 $247.70   5.105%   $260.3451   $260.35   $260.35   $260.30  
  Purchase #6 $18.46   10.507%   $20.3996   $20.40   $20.40   $20.40  
  Purchase #7 $16.29   11.321%   $18.1342   $18.13   $18.15   $18.10  
  7 purchase totals = $873.40       $954.4754   $954.48   $954.50   $954.40