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 $247.31   9.423%   $270.614   $270.61   $270.60   $270.60  
  Purchase #2 $158.47   13.793%   $180.3278   $180.33   $180.35   $180.30  
  Purchase #3 $233.93   3.255%   $241.5444   $241.54   $241.55   $241.50  
  Purchase #4 $59.63   6.754%   $63.6574   $63.66   $63.65   $63.70  
  Purchase #5 $206.44   5.246%   $217.2698   $217.27   $217.25   $217.30  
  Purchase #6 $214.43   10.102%   $236.0917   $236.09   $236.10   $236.10  
  Purchase #7 $132.52   7.681%   $142.6989   $142.70   $142.70   $142.70  
  7 purchase totals = $1,252.73       $1,352.2040   $1,352.20   $1,352.20   $1,352.20