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 $58.87   7.160%   $63.0851   $63.09   $63.10   $63.10  
  Purchase #2 $224.71   8.496%   $243.8014   $243.80   $243.80   $243.80  
  Purchase #3 $30.53   6.773%   $32.5978   $32.60   $32.60   $32.60  
  Purchase #4 $206.44   4.228%   $215.1683   $215.17   $215.15   $215.20  
  Purchase #5 $211.74   10.729%   $234.4576   $234.46   $234.45   $234.50  
  Purchase #6 $14.81   8.726%   $16.1023   $16.10   $16.10   $16.10  
  Purchase #7 $170.91   13.828%   $194.5434   $194.54   $194.55   $194.50  
  7 purchase totals = $918.01       $999.7559   $999.76   $999.75   $999.80