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	$195.55	12.802%	$220.5843	$220.58	$220.60	$220.60
Purchase #2	$172.82	9.173%	$188.6728	$188.67	$188.65	$188.70
Purchase #3	$79.33	13.603%	$90.1213	$90.12	$90.10	$90.10
Purchase #4	$145.90	5.177%	$153.4532	$153.45	$153.45	$153.50
Purchase #5	$15.91	13.440%	$18.0483	$18.05	$18.05	$18.00
Purchase #6	$47.49	6.377%	$50.5184	$50.52	$50.50	$50.50
Purchase #7	$16.71	13.476%	$18.9618	$18.96	$18.95	$19.00
7 purchase totals =	$673.71		$740.3601	$740.35	$740.30	$740.40