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	$74.45	11.574%	$83.0668	$83.07	$83.05	$83.10
Purchase #2	$86.45	13.136%	$97.8061	$97.81	$97.80	$97.80
Purchase #3	$43.63	10.191%	$48.0763	$48.08	$48.10	$48.10
Purchase #4	$174.89	5.261%	$184.091	$184.09	$184.10	$184.10
Purchase #5	$123.50	6.470%	$131.4905	$131.49	$131.50	$131.50
Purchase #6	$21.66	3.113%	$22.3343	$22.33	$22.35	$22.30
Purchase #7	$27.31	4.679%	$28.5878	$28.59	$28.60	$28.60
7 purchase totals =	$551.89		$595.4528	$595.46	$595.50	$595.50