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 $217.88   10.228%   $240.1648   $240.16   $240.15   $240.20  
  Purchase #2 $195.38   4.862%   $204.8794   $204.88   $204.90   $204.90  
  Purchase #3 $52.77   3.169%   $54.4423   $54.44   $54.45   $54.40  
  Purchase #4 $117.95   5.354%   $124.265   $124.27   $124.25   $124.30  
  Purchase #5 $23.83   4.798%   $24.9734   $24.97   $24.95   $25.00  
  Purchase #6 $66.35   8.400%   $71.9234   $71.92   $71.90   $71.90  
  Purchase #7 $35.67   10.318%   $39.3504   $39.35   $39.35   $39.40  
  7 purchase totals = $709.83       $759.9987   $759.99   $759.95   $760.10