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	$120.34	5.328%	$126.7517	$126.75	$126.75	$126.80
Purchase #2	$182.33	10.145%	$200.8274	$200.83	$200.85	$200.80
Purchase #3	$108.90	7.364%	$116.9194	$116.92	$116.90	$116.90
Purchase #4	$50.26	7.439%	$53.9988	$54.00	$54.00	$54.00
Purchase #5	$29.43	13.454%	$33.3895	$33.39	$33.40	$33.40
Purchase #6	$53.66	3.413%	$55.4914	$55.49	$55.50	$55.50
Purchase #7	$45.45	13.717%	$51.6844	$51.68	$51.70	$51.70
7 purchase totals =	$590.37		$639.0626	$639.06	$639.10	$639.10