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	$75.66	6.116%	$80.2874	$80.29	$80.30	$80.30
Purchase #2	$126.82	9.824%	$139.2788	$139.28	$139.30	$139.30
Purchase #3	$19.80	12.181%	$22.2118	$22.21	$22.20	$22.20
Purchase #4	$238.52	12.122%	$267.4334	$267.43	$267.45	$267.40
Purchase #5	$40.52	13.275%	$45.899	$45.90	$45.90	$45.90
Purchase #6	$94.78	4.525%	$99.0688	$99.07	$99.05	$99.10
Purchase #7	$123.38	9.352%	$134.9185	$134.92	$134.90	$134.90
7 purchase totals =	$719.48		$789.0977	$789.10	$789.10	$789.10