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 $14.61   13.569%   $16.5924   $16.59   $16.60   $16.60  
  Purchase #2 $234.75   13.269%   $265.899   $265.90   $265.90   $265.90  
  Purchase #3 $240.95   11.468%   $268.5821   $268.58   $268.60   $268.60  
  Purchase #4 $163.35   6.873%   $174.577   $174.58   $174.60   $174.60  
  Purchase #5 $107.38   11.191%   $119.3969   $119.40   $119.40   $119.40  
  Purchase #6 $182.83   4.797%   $191.6004   $191.60   $191.60   $191.60  
  Purchase #7 $133.83   4.714%   $140.1387   $140.14   $140.15   $140.10  
  7 purchase totals = $1,077.70       $1,176.7865   $1,176.79   $1,176.85   $1,176.80