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 $56.73   9.778%   $62.2771   $62.28   $62.30   $62.30  
  Purchase #2 $54.78   7.693%   $58.9942   $58.99   $59.00   $59.00  
  Purchase #3 $130.48   3.550%   $135.112   $135.11   $135.10   $135.10  
  Purchase #4 $17.83   6.236%   $18.9419   $18.94   $18.95   $18.90  
  Purchase #5 $168.63   5.704%   $178.2487   $178.25   $178.25   $178.20  
  Purchase #6 $93.30   11.733%   $104.2469   $104.25   $104.25   $104.20  
  Purchase #7 $159.85   4.664%   $167.3054   $167.31   $167.30   $167.30  
  7 purchase totals = $681.60       $725.1262   $725.13   $725.15   $725.00