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 $198.86   4.197%   $207.2062   $207.21   $207.20   $207.20  
  Purchase #2 $93.34   3.592%   $96.6928   $96.69   $96.70   $96.70  
  Purchase #3 $72.71   12.376%   $81.7086   $81.71   $81.70   $81.70  
  Purchase #4 $74.86   12.517%   $84.2302   $84.23   $84.25   $84.20  
  Purchase #5 $229.37   4.754%   $240.2742   $240.27   $240.25   $240.30  
  Purchase #6 $205.37   4.458%   $214.5254   $214.53   $214.55   $214.50  
  Purchase #7 $227.97   7.149%   $244.2676   $244.27   $244.25   $244.30  
  7 purchase totals = $1,102.48       $1,168.9050   $1,168.91   $1,168.90   $1,168.90