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	$26.39	5.303%	$27.7895	$27.79	$27.80	$27.80
Purchase #2	$100.36	3.218%	$103.5896	$103.59	$103.60	$103.60
Purchase #3	$91.64	9.574%	$100.4136	$100.41	$100.40	$100.40
Purchase #4	$250.58	4.760%	$262.5076	$262.51	$262.50	$262.50
Purchase #5	$226.69	3.104%	$233.7265	$233.73	$233.75	$233.70
Purchase #6	$235.42	9.339%	$257.4059	$257.41	$257.40	$257.40
Purchase #7	$239.28	13.140%	$270.7214	$270.72	$270.70	$270.70
7 purchase totals =	$1,170.36		$1,256.1541	$1,256.16	$1,256.15	$1,256.10