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 $59.46   4.830%   $62.3319   $62.33   $62.35   $62.30  
  Purchase #2 $82.75   13.621%   $94.0214   $94.02   $94.00   $94.00  
  Purchase #3 $76.43   10.733%   $84.6332   $84.63   $84.65   $84.60  
  Purchase #4 $188.41   11.853%   $210.7422   $210.74   $210.75   $210.70  
  Purchase #5 $30.28   13.655%   $34.4147   $34.41   $34.40   $34.40  
  Purchase #6 $92.63   4.526%   $96.8224   $96.82   $96.80   $96.80  
  Purchase #7 $147.53   7.143%   $158.0681   $158.07   $158.05   $158.10  
  7 purchase totals = $677.49       $741.0339   $741.02   $741.00   $740.90