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	$83.28	6.251%	$88.4858	$88.49	$88.50	$88.50
Purchase #2	$15.96	11.637%	$17.8173	$17.82	$17.80	$17.80
Purchase #3	$126.50	8.773%	$137.5978	$137.60	$137.60	$137.60
Purchase #4	$82.46	10.134%	$90.8165	$90.82	$90.80	$90.80
Purchase #5	$74.96	13.798%	$85.303	$85.30	$85.30	$85.30
Purchase #6	$222.82	9.324%	$243.5957	$243.60	$243.60	$243.60
Purchase #7	$106.66	3.550%	$110.4464	$110.45	$110.45	$110.40
7 purchase totals =	$712.64		$774.0625	$774.08	$774.05	$774.00