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 $245.55   6.576%   $261.6974   $261.70   $261.70   $261.70  
  Purchase #2 $127.84   9.132%   $139.5143   $139.51   $139.50   $139.50  
  Purchase #3 $73.56   3.415%   $76.0721   $76.07   $76.05   $76.10  
  Purchase #4 $195.31   4.536%   $204.1693   $204.17   $204.15   $204.20  
  Purchase #5 $234.52   10.838%   $259.9373   $259.94   $259.95   $259.90  
  Purchase #6 $244.68   11.619%   $273.1094   $273.11   $273.10   $273.10  
  Purchase #7 $221.32   5.785%   $234.1234   $234.12   $234.10   $234.10  
  7 purchase totals = $1,342.78       $1,448.6232   $1,448.62   $1,448.55   $1,448.60