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	$143.47	9.628%	$157.2833	$157.28	$157.30	$157.30
Purchase #2	$147.47	13.782%	$167.7943	$167.79	$167.80	$167.80
Purchase #3	$129.37	6.623%	$137.9382	$137.94	$137.95	$137.90
Purchase #4	$167.64	10.854%	$185.8356	$185.84	$185.85	$185.80
Purchase #5	$135.65	5.376%	$142.9425	$142.94	$142.95	$142.90
Purchase #6	$57.45	6.429%	$61.1435	$61.14	$61.15	$61.10
Purchase #7	$31.40	4.531%	$32.8227	$32.82	$32.80	$32.80
7 purchase totals =	$812.45		$885.7601	$885.75	$885.80	$885.60