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 $135.90   8.115%   $146.9283   $146.93   $146.95   $146.90  
  Purchase #2 $228.90   9.562%   $250.7874   $250.79   $250.80   $250.80  
  Purchase #3 $232.66   12.590%   $261.9519   $261.95   $261.95   $262.00  
  Purchase #4 $200.66   11.132%   $222.9975   $223.00   $223.00   $223.00  
  Purchase #5 $168.31   11.824%   $188.211   $188.21   $188.20   $188.20  
  Purchase #6 $211.63   6.510%   $225.4071   $225.41   $225.40   $225.40  
  Purchase #7 $193.45   12.488%   $217.608   $217.61   $217.60   $217.60  
  7 purchase totals = $1,371.51       $1,513.8912   $1,513.90   $1,513.90   $1,513.90