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	$210.34	12.348%	$236.3128	$236.31	$236.30	$236.30
Purchase #2	$24.60	11.461%	$27.4194	$27.42	$27.40	$27.40
Purchase #3	$233.26	10.795%	$258.4404	$258.44	$258.45	$258.40
Purchase #4	$135.66	13.627%	$154.1464	$154.15	$154.15	$154.10
Purchase #5	$132.47	5.563%	$139.8393	$139.84	$139.85	$139.80
Purchase #6	$40.34	12.773%	$45.4926	$45.49	$45.50	$45.50
Purchase #7	$136.49	12.213%	$153.1595	$153.16	$153.15	$153.20
7 purchase totals =	$913.16		$1,014.8104	$1,014.81	$1,014.80	$1,014.70