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 $162.80   12.257%   $182.7544   $182.75   $182.75   $182.80  
  Purchase #2 $239.68   13.170%   $271.2459   $271.25   $271.25   $271.20  
  Purchase #3 $48.39   10.643%   $53.5401   $53.54   $53.55   $53.50  
  Purchase #4 $21.76   6.253%   $23.1207   $23.12   $23.10   $23.10  
  Purchase #5 $213.53   4.826%   $223.835   $223.84   $223.85   $223.80  
  Purchase #6 $235.75   10.776%   $261.1544   $261.15   $261.15   $261.20  
  Purchase #7 $215.90   4.563%   $225.7515   $225.75   $225.75   $225.80  
  7 purchase totals = $1,137.81       $1,241.4020   $1,241.40   $1,241.40   $1,241.40