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 $58.60   7.525%   $63.0097   $63.01   $63.00   $63.00  
  Purchase #2 $110.93   9.869%   $121.8777   $121.88   $121.90   $121.90  
  Purchase #3 $213.38   5.227%   $224.5334   $224.53   $224.55   $224.50  
  Purchase #4 $137.74   7.499%   $148.0691   $148.07   $148.05   $148.10  
  Purchase #5 $98.60   6.402%   $104.9124   $104.91   $104.90   $104.90  
  Purchase #6 $71.76   9.105%   $78.2937   $78.29   $78.30   $78.30  
  Purchase #7 $179.39   10.533%   $198.2851   $198.29   $198.30   $198.30  
  7 purchase totals = $870.40       $938.9811   $938.98   $939.00   $939.00