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 $69.38   8.452%   $75.244   $75.24   $75.25   $75.20  
  Purchase #2 $74.78   10.858%   $82.8996   $82.90   $82.90   $82.90  
  Purchase #3 $227.47   5.788%   $240.636   $240.64   $240.65   $240.60  
  Purchase #4 $217.27   11.579%   $242.4277   $242.43   $242.45   $242.40  
  Purchase #5 $63.69   9.842%   $69.9584   $69.96   $69.95   $70.00  
  Purchase #6 $245.76   6.422%   $261.5427   $261.54   $261.55   $261.50  
  Purchase #7 $206.83   3.778%   $214.644   $214.64   $214.65   $214.60  
  7 purchase totals = $1,105.18       $1,187.3524   $1,187.35   $1,187.40   $1,187.20