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	$37.92	6.585%	$40.417	$40.42	$40.40	$40.40
Purchase #2	$44.39	9.863%	$48.7682	$48.77	$48.75	$48.80
Purchase #3	$21.37	3.249%	$22.0643	$22.06	$22.05	$22.10
Purchase #4	$37.99	10.679%	$42.047	$42.05	$42.05	$42.00
Purchase #5	$227.76	11.774%	$254.5765	$254.58	$254.60	$254.60
Purchase #6	$43.51	4.156%	$45.3183	$45.32	$45.30	$45.30
Purchase #7	$51.30	6.489%	$54.6289	$54.63	$54.65	$54.60
7 purchase totals =	$464.24		$507.8202	$507.83	$507.80	$507.80