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 $29.51   13.422%   $33.4708   $33.47   $33.45   $33.50  
  Purchase #2 $168.53   10.428%   $186.1043   $186.10   $186.10   $186.10  
  Purchase #3 $67.54   10.306%   $74.5007   $74.50   $74.50   $74.50  
  Purchase #4 $38.98   3.867%   $40.4874   $40.49   $40.50   $40.50  
  Purchase #5 $82.90   11.345%   $92.305   $92.31   $92.30   $92.30  
  Purchase #6 $197.67   4.727%   $207.0139   $207.01   $207.00   $207.00  
  Purchase #7 $126.56   8.591%   $137.4328   $137.43   $137.45   $137.40  
  7 purchase totals = $711.69       $771.3149   $771.31   $771.30   $771.30