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	$128.56	7.668%	$138.418	$138.42	$138.40	$138.40
Purchase #2	$111.31	13.780%	$126.6485	$126.65	$126.65	$126.60
Purchase #3	$39.87	7.233%	$42.7538	$42.75	$42.75	$42.80
Purchase #4	$222.91	4.223%	$232.3235	$232.32	$232.30	$232.30
Purchase #5	$103.35	7.467%	$111.0671	$111.07	$111.05	$111.10
Purchase #6	$137.78	7.657%	$148.3298	$148.33	$148.35	$148.30
Purchase #7	$157.78	6.418%	$167.9063	$167.91	$167.90	$167.90
7 purchase totals =	$901.56		$967.4470	$967.45	$967.40	$967.40