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 $71.56   6.784%   $76.4146   $76.41   $76.40   $76.40  
  Purchase #2 $158.73   5.630%   $167.6665   $167.67   $167.65   $167.70  
  Purchase #3 $224.45   6.495%   $239.028   $239.03   $239.05   $239.00  
  Purchase #4 $121.51   5.239%   $127.8759   $127.88   $127.90   $127.90  
  Purchase #5 $223.81   5.554%   $236.2404   $236.24   $236.25   $236.20  
  Purchase #6 $217.56   7.276%   $233.3897   $233.39   $233.40   $233.40  
  Purchase #7 $151.70   7.146%   $162.5405   $162.54   $162.55   $162.50  
  7 purchase totals = $1,169.32       $1,243.1556   $1,243.16   $1,243.20   $1,243.10