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	$108.75	13.351%	$123.2692	$123.27	$123.25	$123.30
Purchase #2	$55.54	7.420%	$59.6611	$59.66	$59.65	$59.70
Purchase #3	$241.47	6.320%	$256.7309	$256.73	$256.75	$256.70
Purchase #4	$139.74	5.613%	$147.5836	$147.58	$147.60	$147.60
Purchase #5	$226.54	11.554%	$252.7144	$252.71	$252.70	$252.70
Purchase #6	$158.60	8.158%	$171.5386	$171.54	$171.55	$171.50
Purchase #7	$204.25	5.638%	$215.7656	$215.77	$215.75	$215.80
7 purchase totals =	$1,134.89		$1,227.2634	$1,227.26	$1,227.25	$1,227.30