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 $184.37   13.687%   $209.6047   $209.60   $209.60   $209.60  
  Purchase #2 $59.57   11.105%   $66.1852   $66.19   $66.20   $66.20  
  Purchase #3 $94.80   8.447%   $102.8078   $102.81   $102.80   $102.80  
  Purchase #4 $136.72   7.405%   $146.8441   $146.84   $146.85   $146.80  
  Purchase #5 $73.69   4.742%   $77.1844   $77.18   $77.20   $77.20  
  Purchase #6 $248.71   5.503%   $262.3965   $262.40   $262.40   $262.40  
  Purchase #7 $85.58   6.278%   $90.9527   $90.95   $90.95   $91.00  
  7 purchase totals = $883.44       $955.9754   $955.97   $956.00   $956.00