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	$25.59	10.242%	$28.2109	$28.21	$28.20	$28.20
Purchase #2	$9.83	4.376%	$10.2602	$10.26	$10.25	$10.30
Purchase #3	$160.71	3.556%	$166.4248	$166.42	$166.40	$166.40
Purchase #4	$18.28	4.355%	$19.0761	$19.08	$19.10	$19.10
Purchase #5	$70.41	11.326%	$78.3846	$78.38	$78.40	$78.40
Purchase #6	$243.87	5.330%	$256.8683	$256.87	$256.85	$256.90
Purchase #7	$55.43	4.390%	$57.8634	$57.86	$57.85	$57.90
7 purchase totals =	$584.12		$617.0883	$617.08	$617.05	$617.20