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	$223.70	5.598%	$236.2227	$236.22	$236.20	$236.20
Purchase #2	$196.29	8.402%	$212.7823	$212.78	$212.80	$212.80
Purchase #3	$234.97	10.104%	$258.7114	$258.71	$258.70	$258.70
Purchase #4	$37.51	13.141%	$42.4392	$42.44	$42.45	$42.40
Purchase #5	$157.48	9.767%	$172.8611	$172.86	$172.85	$172.90
Purchase #6	$105.44	12.530%	$118.6516	$118.65	$118.65	$118.70
Purchase #7	$180.75	8.559%	$196.2204	$196.22	$196.20	$196.20
7 purchase totals =	$1,136.14		$1,237.8887	$1,237.88	$1,237.85	$1,237.90