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	$166.32	3.766%	$172.5836	$172.58	$172.60	$172.60
Purchase #2	$148.31	4.569%	$155.0863	$155.09	$155.10	$155.10
Purchase #3	$35.63	9.773%	$39.1121	$39.11	$39.10	$39.10
Purchase #4	$151.96	13.373%	$172.2816	$172.28	$172.30	$172.30
Purchase #5	$136.91	7.831%	$147.6314	$147.63	$147.65	$147.60
Purchase #6	$31.99	11.364%	$35.6253	$35.63	$35.65	$35.60
Purchase #7	$134.74	8.253%	$145.8601	$145.86	$145.85	$145.90
7 purchase totals =	$805.86		$868.1804	$868.18	$868.25	$868.20