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	$10.59	12.686%	$11.9334	$11.93	$11.95	$11.90
Purchase #2	$196.60	6.501%	$209.381	$209.38	$209.40	$209.40
Purchase #3	$90.44	10.662%	$100.0827	$100.08	$100.10	$100.10
Purchase #4	$120.27	8.525%	$130.523	$130.52	$130.50	$130.50
Purchase #5	$145.82	10.249%	$160.7651	$160.77	$160.75	$160.80
Purchase #6	$160.84	3.382%	$166.2796	$166.28	$166.30	$166.30
Purchase #7	$52.77	13.772%	$60.0375	$60.04	$60.05	$60.00
7 purchase totals =	$777.33		$839.0023	$839.00	$839.05	$839.00