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 $198.58   3.619%   $205.7666   $205.77   $205.75   $205.80  
  Purchase #2 $232.66   12.442%   $261.6076   $261.61   $261.60   $261.60  
  Purchase #3 $110.99   12.763%   $125.1557   $125.16   $125.15   $125.20  
  Purchase #4 $35.63   6.473%   $37.9363   $37.94   $37.95   $37.90  
  Purchase #5 $19.62   9.869%   $21.5563   $21.56   $21.55   $21.60  
  Purchase #6 $226.75   9.827%   $249.0327   $249.03   $249.05   $249.00  
  Purchase #7 $64.34   7.169%   $68.9525   $68.95   $68.95   $69.00  
  7 purchase totals = $888.57       $970.0077   $970.02   $970.00   $970.10