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 $52.68   12.736%   $59.3893   $59.39   $59.40   $59.40  
  Purchase #2 $230.80   5.148%   $242.6816   $242.68   $242.70   $242.70  
  Purchase #3 $30.85   10.513%   $34.0933   $34.09   $34.10   $34.10  
  Purchase #4 $187.44   10.638%   $207.3799   $207.38   $207.40   $207.40  
  Purchase #5 $59.43   8.733%   $64.62   $64.62   $64.60   $64.60  
  Purchase #6 $81.45   12.153%   $91.3486   $91.35   $91.35   $91.30  
  Purchase #7 $191.48   13.268%   $216.8856   $216.89   $216.90   $216.90  
  7 purchase totals = $834.13       $916.3983   $916.40   $916.45   $916.40