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 $57.58   6.246%   $61.1764   $61.18   $61.20   $61.20  
  Purchase #2 $146.96   8.523%   $159.4854   $159.49   $159.50   $159.50  
  Purchase #3 $67.30   4.458%   $70.3002   $70.30   $70.30   $70.30  
  Purchase #4 $97.93   3.565%   $101.4212   $101.42   $101.40   $101.40  
  Purchase #5 $133.46   5.763%   $141.1513   $141.15   $141.15   $141.20  
  Purchase #6 $14.58   11.619%   $16.2741   $16.27   $16.25   $16.30  
  Purchase #7 $109.62   7.748%   $118.1134   $118.11   $118.10   $118.10  
  7 purchase totals = $627.43       $667.9220   $667.92   $667.90   $668.00