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	$26.27	9.515%	$28.7696	$28.77	$28.75	$28.80
Purchase #2	$138.78	3.562%	$143.7233	$143.72	$143.70	$143.70
Purchase #3	$93.54	6.722%	$99.8278	$99.83	$99.85	$99.80
Purchase #4	$96.88	11.344%	$107.8701	$107.87	$107.85	$107.90
Purchase #5	$159.69	4.539%	$166.9383	$166.94	$166.95	$166.90
Purchase #6	$233.88	12.833%	$263.8938	$263.89	$263.90	$263.90
Purchase #7	$97.60	11.522%	$108.8455	$108.85	$108.85	$108.80
7 purchase totals =	$846.64		$919.8684	$919.87	$919.85	$919.80