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	$175.99	6.823%	$187.9978	$188.00	$188.00	$188.00
Purchase #2	$205.27	13.738%	$233.47	$233.47	$233.45	$233.50
Purchase #3	$56.90	10.478%	$62.862	$62.86	$62.85	$62.90
Purchase #4	$121.94	8.712%	$132.5634	$132.56	$132.55	$132.60
Purchase #5	$138.63	11.321%	$154.3243	$154.32	$154.30	$154.30
Purchase #6	$160.27	4.121%	$166.8747	$166.87	$166.85	$166.90
Purchase #7	$10.77	4.860%	$11.2934	$11.29	$11.30	$11.30
7 purchase totals =	$869.77		$949.3856	$949.37	$949.30	$949.50