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	$68.97	12.831%	$77.8195	$77.82	$77.80	$77.80
Purchase #2	$25.77	13.545%	$29.2605	$29.26	$29.25	$29.30
Purchase #3	$54.74	12.212%	$61.4248	$61.42	$61.40	$61.40
Purchase #4	$157.55	9.632%	$172.7252	$172.73	$172.75	$172.70
Purchase #5	$47.33	12.585%	$53.2865	$53.29	$53.30	$53.30
Purchase #6	$41.91	10.612%	$46.3575	$46.36	$46.35	$46.40
Purchase #7	$204.63	10.739%	$226.6052	$226.61	$226.60	$226.60
7 purchase totals =	$600.90		$667.4792	$667.49	$667.45	$667.50