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 $214.78   7.651%   $231.2128   $231.21   $231.20   $231.20  
  Purchase #2 $115.25   9.808%   $126.5537   $126.55   $126.55   $126.60  
  Purchase #3 $101.47   10.114%   $111.7327   $111.73   $111.75   $111.70  
  Purchase #4 $125.26   7.383%   $134.5079   $134.51   $134.50   $134.50  
  Purchase #5 $13.78   4.515%   $14.4022   $14.40   $14.40   $14.40  
  Purchase #6 $89.75   7.863%   $96.807   $96.81   $96.80   $96.80  
  Purchase #7 $244.38   3.732%   $253.5003   $253.50   $253.50   $253.50  
  7 purchase totals = $904.67       $968.7166   $968.71   $968.70   $968.70