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	$44.71	8.298%	$48.42	$48.42	$48.40	$48.40
Purchase #2	$32.75	3.784%	$33.9893	$33.99	$34.00	$34.00
Purchase #3	$172.94	3.803%	$179.5169	$179.52	$179.50	$179.50
Purchase #4	$120.45	8.665%	$130.887	$130.89	$130.90	$130.90
Purchase #5	$48.70	12.864%	$54.9648	$54.96	$54.95	$55.00
Purchase #6	$99.63	9.795%	$109.3888	$109.39	$109.40	$109.40
Purchase #7	$64.45	11.155%	$71.6394	$71.64	$71.65	$71.60
7 purchase totals =	$583.63		$628.8062	$628.81	$628.80	$628.80