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	$132.84	13.354%	$150.5795	$150.58	$150.60	$150.60
Purchase #2	$97.50	8.251%	$105.5447	$105.54	$105.55	$105.50
Purchase #3	$123.97	5.382%	$130.6421	$130.64	$130.65	$130.60
Purchase #4	$205.85	5.703%	$217.5896	$217.59	$217.60	$217.60
Purchase #5	$53.91	13.337%	$61.1	$61.10	$61.10	$61.10
Purchase #6	$37.69	13.744%	$42.8701	$42.87	$42.85	$42.90
Purchase #7	$166.54	7.371%	$178.8157	$178.82	$178.80	$178.80
7 purchase totals =	$818.30		$887.1417	$887.14	$887.15	$887.10