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	$138.87	3.138%	$143.2277	$143.23	$143.25	$143.20
Purchase #2	$32.69	8.410%	$35.4392	$35.44	$35.45	$35.40
Purchase #3	$131.72	13.121%	$149.003	$149.00	$149.00	$149.00
Purchase #4	$136.75	10.832%	$151.5628	$151.56	$151.55	$151.60
Purchase #5	$12.93	12.322%	$14.5232	$14.52	$14.50	$14.50
Purchase #6	$174.29	6.530%	$185.6711	$185.67	$185.65	$185.70
Purchase #7	$40.47	10.630%	$44.772	$44.77	$44.75	$44.80
7 purchase totals =	$667.72		$724.1990	$724.19	$724.15	$724.20