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 $14.58   4.659%   $15.2593   $15.26   $15.25   $15.30  
  Purchase #2 $96.89   7.540%   $104.1955   $104.20   $104.20   $104.20  
  Purchase #3 $119.51   11.247%   $132.9513   $132.95   $132.95   $133.00  
  Purchase #4 $74.36   3.539%   $76.9916   $76.99   $77.00   $77.00  
  Purchase #5 $107.49   8.187%   $116.2902   $116.29   $116.30   $116.30  
  Purchase #6 $31.93   3.821%   $33.15   $33.15   $33.15   $33.20  
  Purchase #7 $122.65   5.822%   $129.7907   $129.79   $129.80   $129.80  
  7 purchase totals = $567.41       $608.6286   $608.63   $608.65   $608.80