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	$250.72	11.393%	$279.2845	$279.28	$279.30	$279.30
Purchase #2	$195.85	13.348%	$221.9921	$221.99	$222.00	$222.00
Purchase #3	$90.75	12.120%	$101.7489	$101.75	$101.75	$101.70
Purchase #4	$82.79	8.521%	$89.8445	$89.84	$89.85	$89.80
Purchase #5	$18.62	10.871%	$20.6442	$20.64	$20.65	$20.60
Purchase #6	$35.64	13.683%	$40.5166	$40.52	$40.50	$40.50
Purchase #7	$37.53	13.680%	$42.6641	$42.66	$42.65	$42.70
7 purchase totals =	$711.90		$796.6949	$796.68	$796.70	$796.60