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	$129.25	12.282%	$145.1245	$145.12	$145.10	$145.10
Purchase #2	$46.34	4.624%	$48.4828	$48.48	$48.50	$48.50
Purchase #3	$147.68	12.800%	$166.583	$166.58	$166.60	$166.60
Purchase #4	$64.87	10.568%	$71.7255	$71.73	$71.75	$71.70
Purchase #5	$16.27	12.856%	$18.3617	$18.36	$18.35	$18.40
Purchase #6	$200.45	13.550%	$227.611	$227.61	$227.60	$227.60
Purchase #7	$133.70	9.861%	$146.8842	$146.88	$146.90	$146.90
7 purchase totals =	$738.56		$824.7727	$824.76	$824.80	$824.80