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	$116.70	9.432%	$127.7071	$127.71	$127.70	$127.70
Purchase #2	$54.67	8.569%	$59.3547	$59.35	$59.35	$59.40
Purchase #3	$33.48	5.174%	$35.2123	$35.21	$35.20	$35.20
Purchase #4	$142.27	4.850%	$149.1701	$149.17	$149.15	$149.20
Purchase #5	$105.52	11.528%	$117.6843	$117.68	$117.70	$117.70
Purchase #6	$35.94	10.374%	$39.6684	$39.67	$39.65	$39.70
Purchase #7	$54.98	12.318%	$61.7524	$61.75	$61.75	$61.80
7 purchase totals =	$543.56		$590.5493	$590.54	$590.50	$590.70