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 $211.86   13.738%   $240.9653   $240.97   $240.95   $241.00  
  Purchase #2 $192.32   10.677%   $212.854   $212.85   $212.85   $212.90  
  Purchase #3 $223.95   8.232%   $242.3856   $242.39   $242.40   $242.40  
  Purchase #4 $237.77   7.710%   $256.1021   $256.10   $256.10   $256.10  
  Purchase #5 $155.45   4.681%   $162.7266   $162.73   $162.75   $162.70  
  Purchase #6 $119.78   9.260%   $130.8716   $130.87   $130.85   $130.90  
  Purchase #7 $245.52   6.597%   $261.717   $261.72   $261.70   $261.70  
  7 purchase totals = $1,386.65       $1,507.6222   $1,507.63   $1,507.60   $1,507.70