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 $223.36   9.468%   $244.5077   $244.51   $244.50   $244.50  
  Purchase #2 $90.63   7.795%   $97.6946   $97.69   $97.70   $97.70  
  Purchase #3 $219.44   8.281%   $237.6118   $237.61   $237.60   $237.60  
  Purchase #4 $163.73   6.556%   $174.4641   $174.46   $174.45   $174.50  
  Purchase #5 $27.78   4.642%   $29.0695   $29.07   $29.05   $29.10  
  Purchase #6 $213.57   4.249%   $222.6446   $222.64   $222.65   $222.60  
  Purchase #7 $242.49   3.307%   $250.5091   $250.51   $250.50   $250.50  
  7 purchase totals = $1,181.00       $1,256.5014   $1,256.49   $1,256.45   $1,256.50