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 $69.86   9.265%   $76.3325   $76.33   $76.35   $76.30  
  Purchase #2 $244.83   11.212%   $272.2803   $272.28   $272.30   $272.30  
  Purchase #3 $125.80   5.107%   $132.2246   $132.22   $132.20   $132.20  
  Purchase #4 $121.37   6.505%   $129.2651   $129.27   $129.25   $129.30  
  Purchase #5 $236.72   10.633%   $261.8904   $261.89   $261.90   $261.90  
  Purchase #6 $132.84   3.565%   $137.5757   $137.58   $137.60   $137.60  
  Purchase #7 $229.35   8.124%   $247.9824   $247.98   $248.00   $248.00  
  7 purchase totals = $1,160.77       $1,257.5510   $1,257.55   $1,257.60   $1,257.60