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 $242.98   8.266%   $263.0647   $263.06   $263.05   $263.10  
  Purchase #2 $209.93   3.156%   $216.5554   $216.56   $216.55   $216.60  
  Purchase #3 $185.59   7.160%   $198.8782   $198.88   $198.90   $198.90  
  Purchase #4 $216.33   9.374%   $236.6088   $236.61   $236.60   $236.60  
  Purchase #5 $8.30   5.559%   $8.7614   $8.76   $8.75   $8.80  
  Purchase #6 $15.73   10.483%   $17.379   $17.38   $17.40   $17.40  
  Purchase #7 $167.35   11.361%   $186.3626   $186.36   $186.35   $186.40  
  7 purchase totals = $1,046.21       $1,127.6101   $1,127.61   $1,127.60   $1,127.80