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 $237.66   3.388%   $245.7119   $245.71   $245.70   $245.70  
  Purchase #2 $190.62   13.165%   $215.7151   $215.72   $215.70   $215.70  
  Purchase #3 $86.55   10.770%   $95.8714   $95.87   $95.85   $95.90  
  Purchase #4 $117.82   5.469%   $124.2636   $124.26   $124.25   $124.30  
  Purchase #5 $116.66   12.805%   $131.5983   $131.60   $131.60   $131.60  
  Purchase #6 $185.75   3.460%   $192.177   $192.18   $192.20   $192.20  
  Purchase #7 $41.42   13.245%   $46.9061   $46.91   $46.90   $46.90  
  7 purchase totals = $976.48       $1,052.2434   $1,052.25   $1,052.20   $1,052.30