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 $58.39   12.464%   $65.6677   $65.67   $65.65   $65.70  
  Purchase #2 $229.49   10.604%   $253.8251   $253.83   $253.85   $253.80  
  Purchase #3 $131.94   3.632%   $136.7321   $136.73   $136.75   $136.70  
  Purchase #4 $213.41   3.852%   $221.6306   $221.63   $221.65   $221.60  
  Purchase #5 $233.38   4.551%   $244.0011   $244.00   $244.00   $244.00  
  Purchase #6 $50.95   7.758%   $54.9027   $54.90   $54.90   $54.90  
  Purchase #7 $42.34   11.218%   $47.0897   $47.09   $47.10   $47.10  
  7 purchase totals = $959.90       $1,023.8490   $1,023.85   $1,023.90   $1,023.80