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 $56.49   12.359%   $63.4716   $63.47   $63.45   $63.50  
  Purchase #2 $50.30   3.823%   $52.223   $52.22   $52.20   $52.20  
  Purchase #3 $70.62   9.679%   $77.4553   $77.46   $77.45   $77.50  
  Purchase #4 $195.76   5.475%   $206.4779   $206.48   $206.50   $206.50  
  Purchase #5 $83.65   13.153%   $94.6525   $94.65   $94.65   $94.70  
  Purchase #6 $185.32   12.412%   $208.3219   $208.32   $208.30   $208.30  
  Purchase #7 $95.76   9.543%   $104.8984   $104.90   $104.90   $104.90  
  7 purchase totals = $737.90       $807.5006   $807.50   $807.45   $807.60