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	$144.65	6.684%	$154.3184	$154.32	$154.30	$154.30
Purchase #2	$223.30	6.852%	$238.6005	$238.60	$238.60	$238.60
Purchase #3	$86.87	5.333%	$91.5028	$91.50	$91.50	$91.50
Purchase #4	$221.96	12.668%	$250.0779	$250.08	$250.10	$250.10
Purchase #5	$66.40	6.296%	$70.5805	$70.58	$70.60	$70.60
Purchase #6	$15.31	12.256%	$17.1864	$17.19	$17.20	$17.20
Purchase #7	$249.85	3.726%	$259.1594	$259.16	$259.15	$259.20
7 purchase totals =	$1,008.34		$1,081.4259	$1,081.43	$1,081.45	$1,081.50