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	$181.41	4.493%	$189.5608	$189.56	$189.55	$189.60
Purchase #2	$7.55	5.368%	$7.9553	$7.96	$7.95	$8.00
Purchase #3	$129.29	6.708%	$137.9628	$137.96	$137.95	$138.00
Purchase #4	$111.98	11.454%	$124.8062	$124.81	$124.80	$124.80
Purchase #5	$60.30	8.697%	$65.5443	$65.54	$65.55	$65.50
Purchase #6	$181.78	4.752%	$190.4182	$190.42	$190.40	$190.40
Purchase #7	$81.74	9.609%	$89.5944	$89.59	$89.60	$89.60
7 purchase totals =	$754.05		$805.8420	$805.84	$805.80	$805.90