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	$42.69	6.454%	$45.4452	$45.45	$45.45	$45.40
Purchase #2	$105.72	10.697%	$117.0289	$117.03	$117.05	$117.00
Purchase #3	$184.92	7.573%	$198.924	$198.92	$198.90	$198.90
Purchase #4	$30.72	11.131%	$34.1394	$34.14	$34.15	$34.10
Purchase #5	$93.30	10.868%	$103.4398	$103.44	$103.45	$103.40
Purchase #6	$220.51	13.595%	$250.4883	$250.49	$250.50	$250.50
Purchase #7	$166.81	3.625%	$172.8569	$172.86	$172.85	$172.90
7 purchase totals =	$844.67		$922.3225	$922.33	$922.35	$922.20