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 $167.98   8.779%   $182.727   $182.73   $182.75   $182.70  
  Purchase #2 $131.70   11.302%   $146.5847   $146.58   $146.60   $146.60  
  Purchase #3 $73.32   4.238%   $76.4273   $76.43   $76.45   $76.40  
  Purchase #4 $191.88   3.121%   $197.8686   $197.87   $197.85   $197.90  
  Purchase #5 $56.99   13.227%   $64.5281   $64.53   $64.55   $64.50  
  Purchase #6 $162.34   12.844%   $183.1909   $183.19   $183.20   $183.20  
  Purchase #7 $129.61   8.566%   $140.7124   $140.71   $140.70   $140.70  
  7 purchase totals = $913.82       $992.0390   $992.04   $992.10   $992.00