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 $243.73   4.649%   $255.061   $255.06   $255.05   $255.10  
  Purchase #2 $101.80   12.551%   $114.5769   $114.58   $114.60   $114.60  
  Purchase #3 $6.43   3.262%   $6.6397   $6.64   $6.65   $6.60  
  Purchase #4 $206.64   4.494%   $215.9264   $215.93   $215.95   $215.90  
  Purchase #5 $141.43   7.584%   $152.1561   $152.16   $152.15   $152.20  
  Purchase #6 $62.31   12.311%   $69.981   $69.98   $70.00   $70.00  
  Purchase #7 $130.46   4.491%   $136.319   $136.32   $136.30   $136.30  
  7 purchase totals = $892.80       $950.6601   $950.67   $950.70   $950.70