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 $178.43   10.257%   $196.7316   $196.73   $196.75   $196.70  
  Purchase #2 $182.47   9.529%   $199.8576   $199.86   $199.85   $199.90  
  Purchase #3 $250.46   4.201%   $260.9818   $260.98   $261.00   $261.00  
  Purchase #4 $210.94   5.851%   $223.2821   $223.28   $223.30   $223.30  
  Purchase #5 $69.47   13.373%   $78.7602   $78.76   $78.75   $78.80  
  Purchase #6 $247.95   7.273%   $265.9834   $265.98   $266.00   $266.00  
  Purchase #7 $235.37   7.565%   $253.1757   $253.18   $253.20   $253.20  
  7 purchase totals = $1,375.09       $1,478.7724   $1,478.77   $1,478.85   $1,478.90