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 $198.37   9.752%   $217.715   $217.72   $217.70   $217.70  
  Purchase #2 $74.62   3.530%   $77.2541   $77.25   $77.25   $77.30  
  Purchase #3 $68.39   11.468%   $76.233   $76.23   $76.25   $76.20  
  Purchase #4 $57.77   4.103%   $60.1403   $60.14   $60.15   $60.10  
  Purchase #5 $156.73   6.472%   $166.8736   $166.87   $166.85   $166.90  
  Purchase #6 $11.47   10.673%   $12.6942   $12.69   $12.70   $12.70  
  Purchase #7 $132.95   8.356%   $144.0593   $144.06   $144.05   $144.10  
  7 purchase totals = $700.30       $754.9695   $754.96   $754.95   $755.00