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 $216.27   8.541%   $234.7416   $234.74   $234.75   $234.70  
  Purchase #2 $151.60   3.311%   $156.6195   $156.62   $156.60   $156.60  
  Purchase #3 $164.35   11.808%   $183.7564   $183.76   $183.75   $183.80  
  Purchase #4 $242.85   6.651%   $259.002   $259.00   $259.00   $259.00  
  Purchase #5 $234.89   3.117%   $242.2115   $242.21   $242.20   $242.20  
  Purchase #6 $107.38   9.329%   $117.3975   $117.40   $117.40   $117.40  
  Purchase #7 $190.46   12.673%   $214.597   $214.60   $214.60   $214.60  
  7 purchase totals = $1,307.80       $1,408.3255   $1,408.33   $1,408.30   $1,408.30