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	$148.43	4.189%	$154.6477	$154.65	$154.65	$154.60
Purchase #2	$97.47	4.543%	$101.8981	$101.90	$101.90	$101.90
Purchase #3	$116.78	9.222%	$127.5495	$127.55	$127.55	$127.50
Purchase #4	$56.33	5.492%	$59.4236	$59.42	$59.40	$59.40
Purchase #5	$17.60	7.554%	$18.9295	$18.93	$18.95	$18.90
Purchase #6	$65.66	13.174%	$74.31	$74.31	$74.30	$74.30
Purchase #7	$241.34	4.512%	$252.2293	$252.23	$252.25	$252.20
7 purchase totals =	$743.61		$788.9877	$788.99	$789.00	$788.80