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 $73.36   5.577%   $77.4513   $77.45   $77.45   $77.50  
  Purchase #2 $62.79   6.730%   $67.0158   $67.02   $67.00   $67.00  
  Purchase #3 $210.33   7.203%   $225.4801   $225.48   $225.50   $225.50  
  Purchase #4 $57.99   4.549%   $60.628   $60.63   $60.65   $60.60  
  Purchase #5 $125.88   5.258%   $132.4988   $132.50   $132.50   $132.50  
  Purchase #6 $49.33   11.710%   $55.1065   $55.11   $55.10   $55.10  
  Purchase #7 $96.74   7.694%   $104.1832   $104.18   $104.20   $104.20  
  7 purchase totals = $676.42       $722.3637   $722.37   $722.40   $722.40