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 $197.30   10.288%   $217.5982   $217.60   $217.60   $217.60  
  Purchase #2 $100.72   6.183%   $106.9475   $106.95   $106.95   $106.90  
  Purchase #3 $233.69   4.547%   $244.3159   $244.32   $244.30   $244.30  
  Purchase #4 $215.36   10.177%   $237.2772   $237.28   $237.30   $237.30  
  Purchase #5 $119.91   13.802%   $136.46   $136.46   $136.45   $136.50  
  Purchase #6 $242.32   8.729%   $263.4721   $263.47   $263.45   $263.50  
  Purchase #7 $50.56   7.394%   $54.2984   $54.30   $54.30   $54.30  
  7 purchase totals = $1,159.86       $1,260.3693   $1,260.38   $1,260.35   $1,260.40