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 $245.87   9.391%   $268.9597   $268.96   $268.95   $269.00  
  Purchase #2 $222.94   6.304%   $236.9941   $236.99   $237.00   $237.00  
  Purchase #3 $101.61   11.862%   $113.663   $113.66   $113.65   $113.70  
  Purchase #4 $75.87   5.311%   $79.8995   $79.90   $79.90   $79.90  
  Purchase #5 $126.68   8.433%   $137.3629   $137.36   $137.35   $137.40  
  Purchase #6 $164.79   4.534%   $172.2616   $172.26   $172.25   $172.30  
  Purchase #7 $223.96   4.106%   $233.1558   $233.16   $233.15   $233.20  
  7 purchase totals = $1,161.72       $1,242.2966   $1,242.29   $1,242.25   $1,242.50