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	$16.39	13.102%	$18.5374	$18.54	$18.55	$18.50
Purchase #2	$65.39	11.869%	$73.1511	$73.15	$73.15	$73.20
Purchase #3	$33.91	5.533%	$35.7862	$35.79	$35.80	$35.80
Purchase #4	$155.36	12.611%	$174.9524	$174.95	$174.95	$175.00
Purchase #5	$53.64	11.217%	$59.6568	$59.66	$59.65	$59.70
Purchase #6	$158.77	13.653%	$180.4469	$180.45	$180.45	$180.40
Purchase #7	$142.76	3.784%	$148.162	$148.16	$148.15	$148.20
7 purchase totals =	$626.22		$690.6928	$690.70	$690.70	$690.80