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 $196.73   5.104%   $206.7711   $206.77   $206.75   $206.80  
  Purchase #2 $133.60   5.269%   $140.6394   $140.64   $140.65   $140.60  
  Purchase #3 $167.63   12.401%   $188.4178   $188.42   $188.40   $188.40  
  Purchase #4 $88.32   4.601%   $92.3836   $92.38   $92.40   $92.40  
  Purchase #5 $79.58   11.534%   $88.7588   $88.76   $88.75   $88.80  
  Purchase #6 $244.41   5.366%   $257.525   $257.53   $257.55   $257.50  
  Purchase #7 $220.67   12.829%   $248.9798   $248.98   $249.00   $249.00  
  7 purchase totals = $1,130.94       $1,223.4755   $1,223.48   $1,223.50   $1,223.50