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	$154.90	12.274%	$173.9124	$173.91	$173.90	$173.90
Purchase #2	$69.99	11.533%	$78.0619	$78.06	$78.05	$78.10
Purchase #3	$48.58	13.555%	$55.165	$55.17	$55.15	$55.20
Purchase #4	$246.52	9.282%	$269.402	$269.40	$269.40	$269.40
Purchase #5	$165.25	5.804%	$174.8411	$174.84	$174.85	$174.80
Purchase #6	$68.42	4.703%	$71.6378	$71.64	$71.65	$71.60
Purchase #7	$85.74	3.337%	$88.6011	$88.60	$88.60	$88.60
7 purchase totals =	$839.40		$911.6213	$911.62	$911.60	$911.60