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	$18.69	11.431%	$20.8265	$20.83	$20.85	$20.80
Purchase #2	$204.81	6.557%	$218.2394	$218.24	$218.25	$218.20
Purchase #3	$104.29	6.461%	$111.0282	$111.03	$111.05	$111.00
Purchase #4	$122.52	13.465%	$139.0173	$139.02	$139.00	$139.00
Purchase #5	$211.47	6.699%	$225.6364	$225.64	$225.65	$225.60
Purchase #6	$116.52	13.350%	$132.0754	$132.08	$132.10	$132.10
Purchase #7	$48.25	7.629%	$51.931	$51.93	$51.95	$51.90
7 purchase totals =	$826.55		$898.7542	$898.77	$898.85	$898.60