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 $216.81   11.517%   $241.78   $241.78   $241.80   $241.80  
  Purchase #2 $157.25   8.537%   $170.6744   $170.67   $170.65   $170.70  
  Purchase #3 $143.76   10.388%   $158.6938   $158.69   $158.70   $158.70  
  Purchase #4 $55.99   3.842%   $58.1411   $58.14   $58.15   $58.10  
  Purchase #5 $202.97   9.142%   $221.5255   $221.53   $221.55   $221.50  
  Purchase #6 $186.62   4.762%   $195.5068   $195.51   $195.50   $195.50  
  Purchase #7 $173.61   9.292%   $189.7418   $189.74   $189.75   $189.70  
  7 purchase totals = $1,137.01       $1,236.0634   $1,236.06   $1,236.10   $1,236.00