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 $43.43   9.567%   $47.5849   $47.58   $47.60   $47.60  
  Purchase #2 $99.33   13.427%   $112.667   $112.67   $112.65   $112.70  
  Purchase #3 $68.83   13.521%   $78.1365   $78.14   $78.15   $78.10  
  Purchase #4 $84.43   11.738%   $94.3404   $94.34   $94.35   $94.30  
  Purchase #5 $248.63   3.530%   $257.4066   $257.41   $257.40   $257.40  
  Purchase #6 $242.95   10.872%   $269.3635   $269.36   $269.35   $269.40  
  Purchase #7 $46.27   3.183%   $47.7428   $47.74   $47.75   $47.70  
  7 purchase totals = $833.87       $907.2417   $907.24   $907.25   $907.20