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	$35.43	9.313%	$38.7296	$38.73	$38.75	$38.70
Purchase #2	$91.76	13.643%	$104.2788	$104.28	$104.30	$104.30
Purchase #3	$196.83	3.189%	$203.1069	$203.11	$203.10	$203.10
Purchase #4	$64.78	10.174%	$71.3707	$71.37	$71.35	$71.40
Purchase #5	$185.75	5.757%	$196.4436	$196.44	$196.45	$196.40
Purchase #6	$34.45	3.322%	$35.5944	$35.59	$35.60	$35.60
Purchase #7	$69.30	4.132%	$72.1635	$72.16	$72.15	$72.20
7 purchase totals =	$678.30		$721.6875	$721.68	$721.70	$721.70