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	$143.41	7.107%	$153.6021	$153.60	$153.60	$153.60
Purchase #2	$190.40	13.353%	$215.8241	$215.82	$215.80	$215.80
Purchase #3	$129.66	13.853%	$147.6218	$147.62	$147.60	$147.60
Purchase #4	$100.33	3.217%	$103.5576	$103.56	$103.55	$103.60
Purchase #5	$190.81	4.742%	$199.8582	$199.86	$199.85	$199.90
Purchase #6	$195.32	9.773%	$214.4086	$214.41	$214.40	$214.40
Purchase #7	$228.89	13.209%	$259.1241	$259.12	$259.10	$259.10
7 purchase totals =	$1,178.82		$1,293.9965	$1,293.99	$1,293.90	$1,294.00