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 $228.34   8.722%   $248.2558   $248.26   $248.25   $248.30  
  Purchase #2 $105.46   9.185%   $115.1465   $115.15   $115.15   $115.10  
  Purchase #3 $240.42   3.522%   $248.8876   $248.89   $248.90   $248.90  
  Purchase #4 $32.64   12.132%   $36.5999   $36.60   $36.60   $36.60  
  Purchase #5 $130.91   5.433%   $138.0223   $138.02   $138.00   $138.00  
  Purchase #6 $182.25   7.252%   $195.4668   $195.47   $195.45   $195.50  
  Purchase #7 $231.64   13.798%   $263.6017   $263.60   $263.60   $263.60  
  7 purchase totals = $1,151.66       $1,245.9806   $1,245.99   $1,245.95   $1,246.00