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	$98.49	11.570%	$109.8853	$109.89	$109.90	$109.90
Purchase #2	$71.26	11.709%	$79.6038	$79.60	$79.60	$79.60
Purchase #3	$130.81	12.577%	$147.262	$147.26	$147.25	$147.30
Purchase #4	$107.52	3.502%	$111.2854	$111.29	$111.30	$111.30
Purchase #5	$69.94	11.246%	$77.8055	$77.81	$77.80	$77.80
Purchase #6	$22.45	3.198%	$23.168	$23.17	$23.15	$23.20
Purchase #7	$121.31	8.393%	$131.4915	$131.49	$131.50	$131.50
7 purchase totals =	$621.78		$680.5015	$680.51	$680.50	$680.60