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 $60.82   10.116%   $66.9726   $66.97   $66.95   $67.00  
  Purchase #2 $242.91   13.542%   $275.8049   $275.80   $275.80   $275.80  
  Purchase #3 $11.42   7.288%   $12.2523   $12.25   $12.25   $12.30  
  Purchase #4 $163.38   11.583%   $182.3043   $182.30   $182.30   $182.30  
  Purchase #5 $42.91   12.244%   $48.1639   $48.16   $48.15   $48.20  
  Purchase #6 $64.73   6.228%   $68.7614   $68.76   $68.75   $68.80  
  Purchase #7 $134.63   8.540%   $146.1274   $146.13   $146.15   $146.10  
  7 purchase totals = $720.80       $800.3868   $800.37   $800.35   $800.50