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	$84.75	5.355%	$89.2884	$89.29	$89.30	$89.30
Purchase #2	$86.35	6.133%	$91.6458	$91.65	$91.65	$91.60
Purchase #3	$121.40	4.609%	$126.9953	$127.00	$127.00	$127.00
Purchase #4	$34.45	12.749%	$38.842	$38.84	$38.85	$38.80
Purchase #5	$35.90	11.169%	$39.9097	$39.91	$39.90	$39.90
Purchase #6	$16.77	10.831%	$18.5864	$18.59	$18.60	$18.60
Purchase #7	$101.79	3.841%	$105.6998	$105.70	$105.70	$105.70
7 purchase totals =	$481.41		$510.9674	$510.98	$511.00	$510.90