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	$34.94	11.106%	$38.8204	$38.82	$38.80	$38.80
Purchase #2	$38.87	12.285%	$43.6452	$43.65	$43.65	$43.60
Purchase #3	$55.56	10.283%	$61.2732	$61.27	$61.25	$61.30
Purchase #4	$93.33	9.860%	$102.5323	$102.53	$102.55	$102.50
Purchase #5	$55.42	9.721%	$60.8074	$60.81	$60.80	$60.80
Purchase #6	$127.49	13.783%	$145.0619	$145.06	$145.05	$145.10
Purchase #7	$178.81	8.431%	$193.8855	$193.89	$193.90	$193.90
7 purchase totals =	$584.42		$646.0259	$646.03	$646.00	$646.00