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	$150.59	6.273%	$160.0365	$160.04	$160.05	$160.00
Purchase #2	$27.32	3.861%	$28.3748	$28.37	$28.35	$28.40
Purchase #3	$150.93	9.594%	$165.4102	$165.41	$165.40	$165.40
Purchase #4	$44.30	11.852%	$49.5504	$49.55	$49.55	$49.60
Purchase #5	$103.51	7.571%	$111.3467	$111.35	$111.35	$111.30
Purchase #6	$67.76	7.418%	$72.7864	$72.79	$72.80	$72.80
Purchase #7	$16.95	13.685%	$19.2696	$19.27	$19.25	$19.30
7 purchase totals =	$561.36		$606.7746	$606.78	$606.75	$606.80