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 $175.61   13.295%   $198.9573   $198.96   $198.95   $199.00  
  Purchase #2 $64.53   12.106%   $72.342   $72.34   $72.35   $72.30  
  Purchase #3 $38.89   13.605%   $44.181   $44.18   $44.20   $44.20  
  Purchase #4 $98.51   10.812%   $109.1609   $109.16   $109.15   $109.20  
  Purchase #5 $248.63   11.313%   $276.7575   $276.76   $276.75   $276.80  
  Purchase #6 $163.69   11.829%   $183.0529   $183.05   $183.05   $183.10  
  Purchase #7 $153.25   3.204%   $158.1601   $158.16   $158.15   $158.20  
  7 purchase totals = $943.11       $1,042.6117   $1,042.61   $1,042.60   $1,042.80