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 $66.41   11.663%   $74.1554   $74.16   $74.15   $74.20  
  Purchase #2 $57.28   9.309%   $62.6122   $62.61   $62.60   $62.60  
  Purchase #3 $121.53   3.120%   $125.3217   $125.32   $125.30   $125.30  
  Purchase #4 $189.61   12.338%   $213.0041   $213.00   $213.00   $213.00  
  Purchase #5 $194.88   6.733%   $208.0013   $208.00   $208.00   $208.00  
  Purchase #6 $193.58   4.417%   $202.1304   $202.13   $202.15   $202.10  
  Purchase #7 $67.32   5.275%   $70.8711   $70.87   $70.85   $70.90  
  7 purchase totals = $890.61       $956.0962   $956.09   $956.05   $956.10