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 $208.99   4.202%   $217.7718   $217.77   $217.75   $217.80  
  Purchase #2 $199.41   8.676%   $216.7108   $216.71   $216.70   $216.70  
  Purchase #3 $18.44   7.234%   $19.7739   $19.77   $19.75   $19.80  
  Purchase #4 $56.60   4.704%   $59.2625   $59.26   $59.25   $59.30  
  Purchase #5 $144.90   4.714%   $151.7306   $151.73   $151.75   $151.70  
  Purchase #6 $99.59   10.821%   $110.3666   $110.37   $110.35   $110.40  
  Purchase #7 $228.76   4.627%   $239.3447   $239.34   $239.35   $239.30  
  7 purchase totals = $956.69       $1,014.9609   $1,014.95   $1,014.90   $1,015.00