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 $117.56   6.785%   $125.5364   $125.54   $125.55   $125.50  
  Purchase #2 $113.68   9.777%   $124.7945   $124.79   $124.80   $124.80  
  Purchase #3 $106.40   6.335%   $113.1404   $113.14   $113.15   $113.10  
  Purchase #4 $93.43   5.139%   $98.2314   $98.23   $98.25   $98.20  
  Purchase #5 $20.99   13.718%   $23.8694   $23.87   $23.85   $23.90  
  Purchase #6 $76.77   7.305%   $82.378   $82.38   $82.40   $82.40  
  Purchase #7 $123.90   6.634%   $132.1195   $132.12   $132.10   $132.10  
  7 purchase totals = $652.73       $700.0696   $700.07   $700.10   $700.00