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	$17.84	3.432%	$18.4523	$18.45	$18.45	$18.50
Purchase #2	$42.87	13.614%	$48.7063	$48.71	$48.70	$48.70
Purchase #3	$250.51	12.640%	$282.1745	$282.17	$282.15	$282.20
Purchase #4	$99.38	12.193%	$111.4974	$111.50	$111.50	$111.50
Purchase #5	$172.52	13.821%	$196.364	$196.36	$196.35	$196.40
Purchase #6	$191.34	4.748%	$200.4248	$200.42	$200.40	$200.40
Purchase #7	$179.36	6.522%	$191.0579	$191.06	$191.05	$191.10
7 purchase totals =	$953.82		$1,048.6772	$1,048.67	$1,048.60	$1,048.80