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	$187.45	6.519%	$199.6699	$199.67	$199.65	$199.70
Purchase #2	$107.30	4.500%	$112.1285	$112.13	$112.15	$112.10
Purchase #3	$58.81	13.441%	$66.7147	$66.71	$66.70	$66.70
Purchase #4	$240.92	13.141%	$272.5793	$272.58	$272.60	$272.60
Purchase #5	$92.39	4.430%	$96.4829	$96.48	$96.50	$96.50
Purchase #6	$168.42	6.117%	$178.7223	$178.72	$178.70	$178.70
Purchase #7	$50.46	3.461%	$52.2064	$52.21	$52.20	$52.20
7 purchase totals =	$905.75		$978.5040	$978.50	$978.50	$978.50