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 $62.40   9.472%   $68.3105   $68.31   $68.30   $68.30  
  Purchase #2 $132.86   10.212%   $146.4277   $146.43   $146.45   $146.40  
  Purchase #3 $207.89   3.593%   $215.3595   $215.36   $215.35   $215.40  
  Purchase #4 $73.87   9.126%   $80.6114   $80.61   $80.60   $80.60  
  Purchase #5 $215.45   5.502%   $227.3041   $227.30   $227.30   $227.30  
  Purchase #6 $49.66   4.618%   $51.9533   $51.95   $51.95   $52.00  
  Purchase #7 $83.44   3.544%   $86.3971   $86.40   $86.40   $86.40  
  7 purchase totals = $825.57       $876.3636   $876.36   $876.35   $876.40