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	$55.35	10.737%	$61.2929	$61.29	$61.30	$61.30
Purchase #2	$153.74	8.426%	$166.6941	$166.69	$166.70	$166.70
Purchase #3	$78.37	5.234%	$82.4719	$82.47	$82.45	$82.50
Purchase #4	$16.82	12.187%	$18.8699	$18.87	$18.85	$18.90
Purchase #5	$248.96	12.376%	$279.7713	$279.77	$279.75	$279.80
Purchase #6	$112.58	13.790%	$128.1048	$128.10	$128.10	$128.10
Purchase #7	$136.29	5.223%	$143.4084	$143.41	$143.40	$143.40
7 purchase totals =	$802.11		$880.6133	$880.60	$880.55	$880.70