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	$244.75	11.618%	$273.1851	$273.19	$273.20	$273.20
Purchase #2	$179.90	5.194%	$189.244	$189.24	$189.25	$189.20
Purchase #3	$166.81	3.302%	$172.3181	$172.32	$172.30	$172.30
Purchase #4	$56.60	5.161%	$59.5211	$59.52	$59.50	$59.50
Purchase #5	$99.74	5.426%	$105.1519	$105.15	$105.15	$105.20
Purchase #6	$73.68	5.409%	$77.6654	$77.67	$77.65	$77.70
Purchase #7	$21.92	9.195%	$23.9355	$23.94	$23.95	$23.90
7 purchase totals =	$843.40		$901.0211	$901.03	$901.00	$901.00