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 $58.61   5.149%   $61.6278   $61.63   $61.65   $61.60  
  Purchase #2 $150.39   9.664%   $164.9237   $164.92   $164.90   $164.90  
  Purchase #3 $129.35   8.212%   $139.9722   $139.97   $139.95   $140.00  
  Purchase #4 $234.30   11.139%   $260.3987   $260.40   $260.40   $260.40  
  Purchase #5 $157.85   13.348%   $178.9198   $178.92   $178.90   $178.90  
  Purchase #6 $201.46   4.528%   $210.5821   $210.58   $210.60   $210.60  
  Purchase #7 $227.74   8.606%   $247.3393   $247.34   $247.35   $247.30  
  7 purchase totals = $1,159.70       $1,263.7636   $1,263.76   $1,263.75   $1,263.70