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	$17.45	4.694%	$18.2691	$18.27	$18.25	$18.30
Purchase #2	$129.50	3.874%	$134.5168	$134.52	$134.50	$134.50
Purchase #3	$212.33	10.171%	$233.9261	$233.93	$233.95	$233.90
Purchase #4	$248.29	9.379%	$271.5771	$271.58	$271.60	$271.60
Purchase #5	$157.89	11.656%	$176.2937	$176.29	$176.30	$176.30
Purchase #6	$140.75	12.773%	$158.728	$158.73	$158.75	$158.70
Purchase #7	$73.68	6.225%	$78.2666	$78.27	$78.25	$78.30
7 purchase totals =	$979.89		$1,071.5774	$1,071.59	$1,071.60	$1,071.60