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 $32.64   4.138%   $33.9906   $33.99   $34.00   $34.00  
  Purchase #2 $50.74   11.865%   $56.7603   $56.76   $56.75   $56.80  
  Purchase #3 $180.74   3.389%   $186.8653   $186.87   $186.85   $186.90  
  Purchase #4 $213.41   10.393%   $235.5897   $235.59   $235.60   $235.60  
  Purchase #5 $249.92   11.750%   $279.2856   $279.29   $279.30   $279.30  
  Purchase #6 $55.81   10.827%   $61.8525   $61.85   $61.85   $61.90  
  Purchase #7 $188.97   13.691%   $214.8419   $214.84   $214.85   $214.80  
  7 purchase totals = $972.23       $1,069.1859   $1,069.19   $1,069.20   $1,069.30