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 $66.90   6.789%   $71.4418   $71.44   $71.45   $71.40  
  Purchase #2 $114.87   3.572%   $118.9732   $118.97   $118.95   $119.00  
  Purchase #3 $119.91   3.454%   $124.0517   $124.05   $124.05   $124.10  
  Purchase #4 $189.40   12.536%   $213.1432   $213.14   $213.15   $213.10  
  Purchase #5 $195.66   9.853%   $214.9384   $214.94   $214.95   $214.90  
  Purchase #6 $121.97   12.728%   $137.4943   $137.49   $137.50   $137.50  
  Purchase #7 $58.77   8.129%   $63.5474   $63.55   $63.55   $63.50  
  7 purchase totals = $867.48       $943.5900   $943.58   $943.60   $943.50