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	$150.68	5.701%	$159.2703	$159.27	$159.25	$159.30
Purchase #2	$160.66	4.614%	$168.0729	$168.07	$168.05	$168.10
Purchase #3	$243.94	4.439%	$254.7685	$254.77	$254.75	$254.80
Purchase #4	$48.33	3.728%	$50.1317	$50.13	$50.15	$50.10
Purchase #5	$16.39	13.475%	$18.5986	$18.60	$18.60	$18.60
Purchase #6	$48.40	9.395%	$52.9472	$52.95	$52.95	$52.90
Purchase #7	$148.43	9.538%	$162.5873	$162.59	$162.60	$162.60
7 purchase totals =	$816.83		$866.3765	$866.38	$866.35	$866.40