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 $53.92   11.783%   $60.2734   $60.27   $60.25   $60.30  
  Purchase #2 $67.73   12.125%   $75.9423   $75.94   $75.95   $75.90  
  Purchase #3 $53.76   9.662%   $58.9543   $58.95   $58.95   $59.00  
  Purchase #4 $89.57   7.451%   $96.2439   $96.24   $96.25   $96.20  
  Purchase #5 $71.60   6.826%   $76.4874   $76.49   $76.50   $76.50  
  Purchase #6 $139.48   6.837%   $149.0162   $149.02   $149.00   $149.00  
  Purchase #7 $205.95   10.680%   $227.9455   $227.95   $227.95   $227.90  
  7 purchase totals = $682.01       $744.8630   $744.86   $744.85   $744.80