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 $23.60   11.182%   $26.239   $26.24   $26.25   $26.20  
  Purchase #2 $249.84   6.804%   $266.8391   $266.84   $266.85   $266.80  
  Purchase #3 $184.75   5.701%   $195.2826   $195.28   $195.30   $195.30  
  Purchase #4 $34.64   4.253%   $36.1132   $36.11   $36.10   $36.10  
  Purchase #5 $93.61   11.440%   $104.319   $104.32   $104.30   $104.30  
  Purchase #6 $195.59   11.601%   $218.2804   $218.28   $218.30   $218.30  
  Purchase #7 $13.99   10.573%   $15.4692   $15.47   $15.45   $15.50  
  7 purchase totals = $796.02       $862.5425   $862.54   $862.55   $862.50