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 $214.76   13.659%   $244.0941   $244.09   $244.10   $244.10  
  Purchase #2 $32.84   8.366%   $35.5874   $35.59   $35.60   $35.60  
  Purchase #3 $54.78   4.493%   $57.2413   $57.24   $57.25   $57.20  
  Purchase #4 $218.90   11.493%   $244.0582   $244.06   $244.05   $244.10  
  Purchase #5 $152.37   3.416%   $157.575   $157.58   $157.60   $157.60  
  Purchase #6 $155.59   3.575%   $161.1523   $161.15   $161.15   $161.20  
  Purchase #7 $65.71   11.820%   $73.4769   $73.48   $73.50   $73.50  
  7 purchase totals = $894.95       $973.1852   $973.19   $973.25   $973.30