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 $125.34   9.495%   $137.241   $137.24   $137.25   $137.20  
  Purchase #2 $46.70   5.485%   $49.2615   $49.26   $49.25   $49.30  
  Purchase #3 $16.27   4.651%   $17.0267   $17.03   $17.05   $17.00  
  Purchase #4 $187.87   4.194%   $195.7493   $195.75   $195.75   $195.70  
  Purchase #5 $114.58   12.796%   $129.2417   $129.24   $129.25   $129.20  
  Purchase #6 $187.80   4.418%   $196.097   $196.10   $196.10   $196.10  
  Purchase #7 $176.34   3.345%   $182.2386   $182.24   $182.25   $182.20  
  7 purchase totals = $854.90       $906.8558   $906.86   $906.90   $906.70