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 $92.78   12.129%   $104.0333   $104.03   $104.05   $104.00  
  Purchase #2 $167.78   12.615%   $188.9454   $188.95   $188.95   $188.90  
  Purchase #3 $151.87   4.615%   $158.8788   $158.88   $158.90   $158.90  
  Purchase #4 $210.40   13.276%   $238.3327   $238.33   $238.35   $238.30  
  Purchase #5 $11.47   5.233%   $12.0702   $12.07   $12.05   $12.10  
  Purchase #6 $136.38   13.137%   $154.2962   $154.30   $154.30   $154.30  
  Purchase #7 $70.94   6.303%   $75.4113   $75.41   $75.40   $75.40  
  7 purchase totals = $841.62       $931.9679   $931.97   $932.00   $931.90