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 $208.63   9.689%   $228.8442   $228.84   $228.85   $228.80  
  Purchase #2 $250.34   10.237%   $275.9673   $275.97   $275.95   $276.00  
  Purchase #3 $248.35   5.175%   $261.2021   $261.20   $261.20   $261.20  
  Purchase #4 $75.27   5.630%   $79.5077   $79.51   $79.50   $79.50  
  Purchase #5 $225.47   12.703%   $254.1115   $254.11   $254.10   $254.10  
  Purchase #6 $107.25   3.153%   $110.6316   $110.63   $110.65   $110.60  
  Purchase #7 $42.81   13.686%   $48.669   $48.67   $48.65   $48.70  
  7 purchase totals = $1,158.12       $1,258.9334   $1,258.93   $1,258.90   $1,258.90