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 $195.91   8.826%   $213.201   $213.20   $213.20   $213.20  
  Purchase #2 $221.28   9.113%   $241.4452   $241.45   $241.45   $241.40  
  Purchase #3 $50.95   5.280%   $53.6402   $53.64   $53.65   $53.60  
  Purchase #4 $248.49   3.745%   $257.796   $257.80   $257.80   $257.80  
  Purchase #5 $32.68   8.453%   $35.4424   $35.44   $35.45   $35.40  
  Purchase #6 $35.68   6.414%   $37.9685   $37.97   $37.95   $38.00  
  Purchase #7 $17.60   3.710%   $18.253   $18.25   $18.25   $18.30  
  7 purchase totals = $802.59       $857.7463   $857.75   $857.75   $857.70