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	$29.72	5.137%	$31.2467	$31.25	$31.25	$31.20
Purchase #2	$161.76	6.390%	$172.0965	$172.10	$172.10	$172.10
Purchase #3	$20.44	4.375%	$21.3343	$21.33	$21.35	$21.30
Purchase #4	$140.29	9.703%	$153.9023	$153.90	$153.90	$153.90
Purchase #5	$136.90	10.863%	$151.7714	$151.77	$151.75	$151.80
Purchase #6	$90.55	12.180%	$101.579	$101.58	$101.60	$101.60
Purchase #7	$18.64	5.852%	$19.7308	$19.73	$19.75	$19.70
7 purchase totals =	$598.30		$651.6610	$651.66	$651.70	$651.60