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 $71.36   7.142%   $76.4565   $76.46   $76.45   $76.50  
  Purchase #2 $249.99   4.725%   $261.802   $261.80   $261.80   $261.80  
  Purchase #3 $52.66   7.486%   $56.6021   $56.60   $56.60   $56.60  
  Purchase #4 $103.43   13.304%   $117.1903   $117.19   $117.20   $117.20  
  Purchase #5 $70.32   12.644%   $79.2113   $79.21   $79.20   $79.20  
  Purchase #6 $203.61   11.747%   $227.5281   $227.53   $227.55   $227.50  
  Purchase #7 $79.91   6.861%   $85.3926   $85.39   $85.40   $85.40  
  7 purchase totals = $831.28       $904.1829   $904.18   $904.20   $904.20