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	$50.48	10.848%	$55.9561	$55.96	$55.95	$56.00
Purchase #2	$37.62	3.417%	$38.9055	$38.91	$38.90	$38.90
Purchase #3	$81.46	3.117%	$83.9991	$84.00	$84.00	$84.00
Purchase #4	$127.92	11.400%	$142.5029	$142.50	$142.50	$142.50
Purchase #5	$166.33	9.540%	$182.1979	$182.20	$182.20	$182.20
Purchase #6	$33.65	4.147%	$35.0455	$35.05	$35.05	$35.00
Purchase #7	$91.79	9.367%	$100.388	$100.39	$100.40	$100.40
7 purchase totals =	$589.25		$638.9950	$639.01	$639.00	$639.00