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	$144.38	8.187%	$156.2004	$156.20	$156.20	$156.20
Purchase #2	$23.58	13.540%	$26.7727	$26.77	$26.75	$26.80
Purchase #3	$118.84	7.397%	$127.6306	$127.63	$127.65	$127.60
Purchase #4	$194.44	12.488%	$218.7217	$218.72	$218.70	$218.70
Purchase #5	$173.34	10.433%	$191.4246	$191.42	$191.40	$191.40
Purchase #6	$102.81	9.822%	$112.908	$112.91	$112.90	$112.90
Purchase #7	$214.78	6.285%	$228.2789	$228.28	$228.30	$228.30
7 purchase totals =	$972.17		$1,061.9369	$1,061.93	$1,061.90	$1,061.90