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 $61.57   11.568%   $68.6924   $68.69   $68.70   $68.70  
  Purchase #2 $30.26   8.493%   $32.83   $32.83   $32.85   $32.80  
  Purchase #3 $142.76   9.247%   $155.961   $155.96   $155.95   $156.00  
  Purchase #4 $193.63   6.447%   $206.1133   $206.11   $206.10   $206.10  
  Purchase #5 $109.43   7.473%   $117.6077   $117.61   $117.60   $117.60  
  Purchase #6 $225.50   8.622%   $244.9426   $244.94   $244.95   $244.90  
  Purchase #7 $14.63   5.772%   $15.4744   $15.47   $15.45   $15.50  
  7 purchase totals = $777.78       $841.6214   $841.61   $841.60   $841.60