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 $56.86   13.306%   $64.4258   $64.43   $64.45   $64.40  
  Purchase #2 $229.99   9.633%   $252.1449   $252.14   $252.15   $252.10  
  Purchase #3 $20.37   5.864%   $21.5645   $21.56   $21.55   $21.60  
  Purchase #4 $87.32   3.622%   $90.4827   $90.48   $90.50   $90.50  
  Purchase #5 $63.26   4.827%   $66.3136   $66.31   $66.30   $66.30  
  Purchase #6 $167.68   11.733%   $187.3539   $187.35   $187.35   $187.40  
  Purchase #7 $101.44   10.644%   $112.2373   $112.24   $112.25   $112.20  
  7 purchase totals = $726.92       $794.5227   $794.51   $794.55   $794.50