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	$19.76	6.526%	$21.0495	$21.05	$21.05	$21.00
Purchase #2	$174.54	11.578%	$194.7482	$194.75	$194.75	$194.70
Purchase #3	$51.44	5.446%	$54.2414	$54.24	$54.25	$54.20
Purchase #4	$67.42	4.725%	$70.6056	$70.61	$70.60	$70.60
Purchase #5	$41.80	11.454%	$46.5878	$46.59	$46.60	$46.60
Purchase #6	$19.29	8.327%	$20.8963	$20.90	$20.90	$20.90
Purchase #7	$68.33	10.453%	$75.4725	$75.47	$75.45	$75.50
7 purchase totals =	$442.58		$483.6013	$483.61	$483.60	$483.50