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	$110.60	5.679%	$116.881	$116.88	$116.90	$116.90
Purchase #2	$141.29	3.700%	$146.5177	$146.52	$146.50	$146.50
Purchase #3	$28.45	13.533%	$32.3001	$32.30	$32.30	$32.30
Purchase #4	$94.82	4.860%	$99.4283	$99.43	$99.45	$99.40
Purchase #5	$145.28	9.334%	$158.8404	$158.84	$158.85	$158.80
Purchase #6	$123.67	4.123%	$128.7689	$128.77	$128.75	$128.80
Purchase #7	$244.96	5.133%	$257.5338	$257.53	$257.55	$257.50
7 purchase totals =	$889.07		$940.2702	$940.27	$940.30	$940.20