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 $239.35   10.202%   $263.7685   $263.77   $263.75   $263.80  
  Purchase #2 $113.77   4.618%   $119.0239   $119.02   $119.00   $119.00  
  Purchase #3 $184.67   8.267%   $199.9367   $199.94   $199.95   $199.90  
  Purchase #4 $101.28   3.141%   $104.4612   $104.46   $104.45   $104.50  
  Purchase #5 $175.86   11.842%   $196.6853   $196.69   $196.70   $196.70  
  Purchase #6 $209.60   11.525%   $233.7564   $233.76   $233.75   $233.80  
  Purchase #7 $248.39   11.129%   $276.0333   $276.03   $276.05   $276.00  
  7 purchase totals = $1,272.92       $1,393.6653   $1,393.67   $1,393.65   $1,393.70