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 $192.67   8.208%   $208.4844   $208.48   $208.50   $208.50  
  Purchase #2 $232.71   4.788%   $243.8522   $243.85   $243.85   $243.90  
  Purchase #3 $161.73   5.241%   $170.2063   $170.21   $170.20   $170.20  
  Purchase #4 $184.55   6.107%   $195.8205   $195.82   $195.80   $195.80  
  Purchase #5 $75.28   9.210%   $82.2133   $82.21   $82.20   $82.20  
  Purchase #6 $32.84   3.234%   $33.902   $33.90   $33.90   $33.90  
  Purchase #7 $229.54   9.128%   $250.4924   $250.49   $250.50   $250.50  
  7 purchase totals = $1,109.32       $1,184.9711   $1,184.96   $1,184.95   $1,185.00