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 $195.49   9.721%   $214.4936   $214.49   $214.50   $214.50  
  Purchase #2 $115.89   3.240%   $119.6448   $119.64   $119.65   $119.60  
  Purchase #3 $88.81   3.430%   $91.8562   $91.86   $91.85   $91.90  
  Purchase #4 $150.30   3.189%   $155.0931   $155.09   $155.10   $155.10  
  Purchase #5 $46.40   5.841%   $49.1102   $49.11   $49.10   $49.10  
  Purchase #6 $173.45   12.813%   $195.6741   $195.67   $195.65   $195.70  
  Purchase #7 $232.63   12.525%   $261.7669   $261.77   $261.75   $261.80  
  7 purchase totals = $1,002.97       $1,087.6389   $1,087.63   $1,087.60   $1,087.70