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	$56.34	4.443%	$58.8432	$58.84	$58.85	$58.80
Purchase #2	$126.79	12.495%	$142.6324	$142.63	$142.65	$142.60
Purchase #3	$147.91	7.114%	$158.4323	$158.43	$158.45	$158.40
Purchase #4	$208.84	12.194%	$234.3059	$234.31	$234.30	$234.30
Purchase #5	$96.47	3.578%	$99.9217	$99.92	$99.90	$99.90
Purchase #6	$130.38	10.687%	$144.3137	$144.31	$144.30	$144.30
Purchase #7	$101.59	5.656%	$107.3359	$107.34	$107.35	$107.30
7 purchase totals =	$868.32		$945.7851	$945.78	$945.80	$945.60