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 $114.32   10.707%   $126.5602   $126.56   $126.55   $126.60  
  Purchase #2 $108.75   9.320%   $118.8855   $118.89   $118.90   $118.90  
  Purchase #3 $84.97   7.716%   $91.5263   $91.53   $91.55   $91.50  
  Purchase #4 $169.95   7.131%   $182.0691   $182.07   $182.05   $182.10  
  Purchase #5 $79.75   7.321%   $85.5885   $85.59   $85.60   $85.60  
  Purchase #6 $44.87   5.217%   $47.2109   $47.21   $47.20   $47.20  
  Purchase #7 $229.77   7.612%   $247.2601   $247.26   $247.25   $247.30  
  7 purchase totals = $832.38       $899.1006   $899.11   $899.10   $899.20