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	$179.65	5.156%	$188.9128	$188.91	$188.90	$188.90
Purchase #2	$153.91	8.581%	$167.117	$167.12	$167.10	$167.10
Purchase #3	$224.28	11.676%	$250.4669	$250.47	$250.45	$250.50
Purchase #4	$47.61	12.173%	$53.4056	$53.41	$53.40	$53.40
Purchase #5	$111.67	6.342%	$118.7521	$118.75	$118.75	$118.80
Purchase #6	$70.72	10.191%	$77.9271	$77.93	$77.95	$77.90
Purchase #7	$227.81	12.237%	$255.6871	$255.69	$255.70	$255.70
7 purchase totals =	$1,015.65		$1,112.2686	$1,112.28	$1,112.25	$1,112.30