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	$224.52	8.815%	$244.3114	$244.31	$244.30	$244.30
Purchase #2	$34.49	11.801%	$38.5602	$38.56	$38.55	$38.60
Purchase #3	$132.78	5.687%	$140.3312	$140.33	$140.35	$140.30
Purchase #4	$38.65	8.299%	$41.8576	$41.86	$41.85	$41.90
Purchase #5	$167.35	4.695%	$175.2071	$175.21	$175.20	$175.20
Purchase #6	$134.29	12.491%	$151.0642	$151.06	$151.05	$151.10
Purchase #7	$9.47	10.127%	$10.429	$10.43	$10.45	$10.40
7 purchase totals =	$741.55		$801.7607	$801.76	$801.75	$801.80