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 $215.66   13.838%   $245.503   $245.50   $245.50   $245.50  
  Purchase #2 $89.89   6.183%   $95.4479   $95.45   $95.45   $95.40  
  Purchase #3 $88.33   11.404%   $98.4032   $98.40   $98.40   $98.40  
  Purchase #4 $196.72   3.705%   $204.0085   $204.01   $204.00   $204.00  
  Purchase #5 $248.32   9.149%   $271.0388   $271.04   $271.05   $271.00  
  Purchase #6 $224.94   5.778%   $237.937   $237.94   $237.95   $237.90  
  Purchase #7 $234.42   6.745%   $250.2316   $250.23   $250.25   $250.20  
  7 purchase totals = $1,298.28       $1,402.5700   $1,402.57   $1,402.60   $1,402.40