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 $24.93   6.334%   $26.5091   $26.51   $26.50   $26.50  
  Purchase #2 $208.68   13.206%   $236.2383   $236.24   $236.25   $236.20  
  Purchase #3 $36.92   10.275%   $40.7135   $40.71   $40.70   $40.70  
  Purchase #4 $140.96   4.836%   $147.7768   $147.78   $147.80   $147.80  
  Purchase #5 $192.42   11.218%   $214.0057   $214.01   $214.00   $214.00  
  Purchase #6 $202.68   7.867%   $218.6248   $218.62   $218.60   $218.60  
  Purchase #7 $183.92   5.725%   $194.4494   $194.45   $194.45   $194.40  
  7 purchase totals = $990.51       $1,078.3176   $1,078.32   $1,078.30   $1,078.20