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 $248.37   11.145%   $276.0508   $276.05   $276.05   $276.10  
  Purchase #2 $242.79   4.633%   $254.0385   $254.04   $254.05   $254.00  
  Purchase #3 $123.92   5.655%   $130.9277   $130.93   $130.95   $130.90  
  Purchase #4 $233.90   12.218%   $262.4779   $262.48   $262.50   $262.50  
  Purchase #5 $144.25   12.873%   $162.8193   $162.82   $162.80   $162.80  
  Purchase #6 $101.85   12.323%   $114.401   $114.40   $114.40   $114.40  
  Purchase #7 $118.25   6.300%   $125.6998   $125.70   $125.70   $125.70  
  7 purchase totals = $1,213.33       $1,326.4150   $1,326.42   $1,326.45   $1,326.40