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	$107.85	9.858%	$118.4819	$118.48	$118.50	$118.50
Purchase #2	$140.29	3.357%	$144.9995	$145.00	$145.00	$145.00
Purchase #3	$105.63	5.534%	$111.4756	$111.48	$111.50	$111.50
Purchase #4	$23.65	3.341%	$24.4401	$24.44	$24.45	$24.40
Purchase #5	$73.41	13.578%	$83.3776	$83.38	$83.40	$83.40
Purchase #6	$7.97	10.629%	$8.8171	$8.82	$8.80	$8.80
Purchase #7	$159.54	8.717%	$173.4471	$173.45	$173.45	$173.40
7 purchase totals =	$618.34		$665.0389	$665.05	$665.10	$665.00