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	$80.52	10.797%	$89.2137	$89.21	$89.20	$89.20
Purchase #2	$40.40	13.655%	$45.9166	$45.92	$45.90	$45.90
Purchase #3	$152.48	3.207%	$157.37	$157.37	$157.35	$157.40
Purchase #4	$42.88	5.162%	$45.0935	$45.09	$45.10	$45.10
Purchase #5	$246.40	7.660%	$265.2742	$265.27	$265.25	$265.30
Purchase #6	$155.69	10.685%	$172.3255	$172.33	$172.35	$172.30
Purchase #7	$204.41	8.823%	$222.4451	$222.45	$222.45	$222.40
7 purchase totals =	$922.78		$997.6386	$997.64	$997.60	$997.60