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	$146.34	7.436%	$157.2218	$157.22	$157.20	$157.20
Purchase #2	$47.55	12.532%	$53.509	$53.51	$53.50	$53.50
Purchase #3	$244.83	5.156%	$257.4534	$257.45	$257.45	$257.50
Purchase #4	$243.84	4.110%	$253.8618	$253.86	$253.85	$253.90
Purchase #5	$66.50	9.697%	$72.9485	$72.95	$72.95	$72.90
Purchase #6	$73.51	13.477%	$83.4169	$83.42	$83.40	$83.40
Purchase #7	$99.60	5.508%	$105.086	$105.09	$105.10	$105.10
7 purchase totals =	$922.17		$983.4974	$983.50	$983.45	$983.50