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 $238.68   13.312%   $270.4531   $270.45   $270.45   $270.50  
  Purchase #2 $115.52   7.599%   $124.2984   $124.30   $124.30   $124.30  
  Purchase #3 $179.77   3.806%   $186.612   $186.61   $186.60   $186.60  
  Purchase #4 $247.62   5.420%   $261.041   $261.04   $261.05   $261.00  
  Purchase #5 $117.59   6.619%   $125.3733   $125.37   $125.35   $125.40  
  Purchase #6 $232.31   4.344%   $242.4015   $242.40   $242.40   $242.40  
  Purchase #7 $233.37   5.731%   $246.7444   $246.74   $246.75   $246.70  
  7 purchase totals = $1,364.86       $1,456.9237   $1,456.91   $1,456.90   $1,456.90