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	$111.78	4.495%	$116.8045	$116.80	$116.80	$116.80
Purchase #2	$177.34	10.657%	$196.2391	$196.24	$196.25	$196.20
Purchase #3	$30.89	9.515%	$33.8292	$33.83	$33.85	$33.80
Purchase #4	$20.75	9.283%	$22.6762	$22.68	$22.70	$22.70
Purchase #5	$162.43	5.105%	$170.7221	$170.72	$170.70	$170.70
Purchase #6	$172.82	9.659%	$189.5127	$189.51	$189.50	$189.50
Purchase #7	$102.45	10.575%	$113.2841	$113.28	$113.30	$113.30
7 purchase totals =	$778.46		$843.0679	$843.06	$843.10	$843.00