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 $70.49   8.796%   $76.6903   $76.69   $76.70   $76.70  
  Purchase #2 $232.79   9.794%   $255.5895   $255.59   $255.60   $255.60  
  Purchase #3 $78.48   11.232%   $87.2949   $87.29   $87.30   $87.30  
  Purchase #4 $209.65   3.446%   $216.8745   $216.87   $216.85   $216.90  
  Purchase #5 $139.53   5.105%   $146.653   $146.65   $146.65   $146.70  
  Purchase #6 $111.47   5.283%   $117.359   $117.36   $117.35   $117.40  
  Purchase #7 $11.69   6.230%   $12.4183   $12.42   $12.40   $12.40  
  7 purchase totals = $854.10       $912.8795   $912.87   $912.85   $913.00