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 $182.71   6.470%   $194.5313   $194.53   $194.55   $194.50  
  Purchase #2 $221.89   9.175%   $242.2484   $242.25   $242.25   $242.20  
  Purchase #3 $122.51   3.324%   $126.5822   $126.58   $126.60   $126.60  
  Purchase #4 $115.35   10.384%   $127.3279   $127.33   $127.35   $127.30  
  Purchase #5 $234.53   7.117%   $251.2215   $251.22   $251.20   $251.20  
  Purchase #6 $238.46   8.870%   $259.6114   $259.61   $259.60   $259.60  
  Purchase #7 $6.45   3.553%   $6.6792   $6.68   $6.70   $6.70  
  7 purchase totals = $1,121.90       $1,208.2019   $1,208.20   $1,208.25   $1,208.10