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 $55.84   12.214%   $62.6603   $62.66   $62.65   $62.70  
  Purchase #2 $19.65   7.496%   $21.123   $21.12   $21.10   $21.10  
  Purchase #3 $50.61   3.250%   $52.2548   $52.25   $52.25   $52.30  
  Purchase #4 $206.34   4.207%   $215.0207   $215.02   $215.00   $215.00  
  Purchase #5 $45.91   6.609%   $48.9442   $48.94   $48.95   $48.90  
  Purchase #6 $160.94   13.692%   $182.9759   $182.98   $183.00   $183.00  
  Purchase #7 $236.83   4.844%   $248.302   $248.30   $248.30   $248.30  
  7 purchase totals = $776.12       $831.2809   $831.27   $831.25   $831.30