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	$99.95	11.323%	$111.2673	$111.27	$111.25	$111.30
Purchase #2	$131.97	5.180%	$138.806	$138.81	$138.80	$138.80
Purchase #3	$214.44	6.602%	$228.5973	$228.60	$228.60	$228.60
Purchase #4	$181.60	3.759%	$188.4263	$188.43	$188.45	$188.40
Purchase #5	$19.50	4.653%	$20.4073	$20.41	$20.40	$20.40
Purchase #6	$158.52	5.469%	$167.1895	$167.19	$167.20	$167.20
Purchase #7	$120.50	6.670%	$128.5374	$128.54	$128.55	$128.50
7 purchase totals =	$926.48		$983.2311	$983.25	$983.25	$983.20