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	$67.27	7.662%	$72.4242	$72.42	$72.40	$72.40
Purchase #2	$148.95	12.249%	$167.1949	$167.19	$167.20	$167.20
Purchase #3	$179.47	6.585%	$191.2881	$191.29	$191.30	$191.30
Purchase #4	$9.52	4.806%	$9.9775	$9.98	$10.00	$10.00
Purchase #5	$105.44	5.352%	$111.0831	$111.08	$111.10	$111.10
Purchase #6	$44.77	3.164%	$46.1865	$46.19	$46.20	$46.20
Purchase #7	$190.36	13.333%	$215.7407	$215.74	$215.75	$215.70
7 purchase totals =	$745.78		$813.8950	$813.89	$813.95	$813.90