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 $67.50   12.165%   $75.7114   $75.71   $75.70   $75.70  
  Purchase #2 $91.59   13.177%   $103.6588   $103.66   $103.65   $103.70  
  Purchase #3 $76.66   7.206%   $82.1841   $82.18   $82.20   $82.20  
  Purchase #4 $32.89   12.104%   $36.871   $36.87   $36.85   $36.90  
  Purchase #5 $150.62   13.283%   $170.6269   $170.63   $170.65   $170.60  
  Purchase #6 $179.38   10.501%   $198.2167   $198.22   $198.20   $198.20  
  Purchase #7 $206.66   5.170%   $217.3443   $217.34   $217.35   $217.30  
  7 purchase totals = $805.30       $884.6132   $884.61   $884.60   $884.60