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 $208.90   12.309%   $234.6135   $234.61   $234.60   $234.60  
  Purchase #2 $232.39   3.293%   $240.0426   $240.04   $240.05   $240.00  
  Purchase #3 $51.46   4.109%   $53.5745   $53.57   $53.55   $53.60  
  Purchase #4 $200.51   7.224%   $214.9948   $214.99   $215.00   $215.00  
  Purchase #5 $183.87   7.290%   $197.2741   $197.27   $197.25   $197.30  
  Purchase #6 $6.58   12.698%   $7.4155   $7.42   $7.40   $7.40  
  Purchase #7 $101.47   12.631%   $114.2867   $114.29   $114.30   $114.30  
  7 purchase totals = $985.18       $1,062.2017   $1,062.19   $1,062.15   $1,062.20