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	$241.38	5.137%	$253.7797	$253.78	$253.80	$253.80
Purchase #2	$138.59	11.740%	$154.8605	$154.86	$154.85	$154.90
Purchase #3	$49.91	10.664%	$55.2324	$55.23	$55.25	$55.20
Purchase #4	$192.82	10.258%	$212.5995	$212.60	$212.60	$212.60
Purchase #5	$137.97	7.708%	$148.6047	$148.60	$148.60	$148.60
Purchase #6	$10.93	7.603%	$11.761	$11.76	$11.75	$11.80
Purchase #7	$229.30	4.803%	$240.3133	$240.31	$240.30	$240.30
7 purchase totals =	$1,000.90		$1,077.1511	$1,077.14	$1,077.15	$1,077.20