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	$139.70	8.489%	$151.5591	$151.56	$151.55	$151.60
Purchase #2	$74.87	6.837%	$79.9889	$79.99	$80.00	$80.00
Purchase #3	$233.98	7.107%	$250.609	$250.61	$250.60	$250.60
Purchase #4	$141.98	11.691%	$158.5789	$158.58	$158.60	$158.60
Purchase #5	$57.52	11.380%	$64.0658	$64.07	$64.05	$64.10
Purchase #6	$175.87	13.595%	$199.7795	$199.78	$199.80	$199.80
Purchase #7	$135.91	7.621%	$146.2677	$146.27	$146.25	$146.30
7 purchase totals =	$959.83		$1,050.8489	$1,050.86	$1,050.85	$1,051.00