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 $188.44   7.108%   $201.8343   $201.83   $201.85   $201.80  
  Purchase #2 $195.67   12.203%   $219.5476   $219.55   $219.55   $219.50  
  Purchase #3 $78.70   5.161%   $82.7617   $82.76   $82.75   $82.80  
  Purchase #4 $227.93   7.433%   $244.872   $244.87   $244.85   $244.90  
  Purchase #5 $250.69   10.733%   $277.5966   $277.60   $277.60   $277.60  
  Purchase #6 $245.33   13.125%   $277.5296   $277.53   $277.55   $277.50  
  Purchase #7 $244.27   7.853%   $263.4525   $263.45   $263.45   $263.50  
  7 purchase totals = $1,431.03       $1,567.5943   $1,567.59   $1,567.60   $1,567.60