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 $44.34   12.684%   $49.9641   $49.96   $49.95   $50.00  
  Purchase #2 $79.68   4.361%   $83.1548   $83.15   $83.15   $83.20  
  Purchase #3 $193.46   10.823%   $214.3982   $214.40   $214.40   $214.40  
  Purchase #4 $209.50   11.477%   $233.5443   $233.54   $233.55   $233.50  
  Purchase #5 $21.28   11.513%   $23.73   $23.73   $23.75   $23.70  
  Purchase #6 $151.49   13.853%   $172.4759   $172.48   $172.50   $172.50  
  Purchase #7 $236.86   3.383%   $244.873   $244.87   $244.85   $244.90  
  7 purchase totals = $936.61       $1,022.1403   $1,022.13   $1,022.15   $1,022.20