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	$168.63	10.312%	$186.0191	$186.02	$186.00	$186.00
Purchase #2	$160.27	7.766%	$172.7166	$172.72	$172.70	$172.70
Purchase #3	$91.97	8.839%	$100.0992	$100.10	$100.10	$100.10
Purchase #4	$45.89	11.832%	$51.3197	$51.32	$51.30	$51.30
Purchase #5	$78.66	4.522%	$82.217	$82.22	$82.20	$82.20
Purchase #6	$151.69	12.527%	$170.6922	$170.69	$170.70	$170.70
Purchase #7	$217.45	9.286%	$237.6424	$237.64	$237.65	$237.60
7 purchase totals =	$914.56		$1,000.7062	$1,000.71	$1,000.65	$1,000.60