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	$112.46	8.388%	$121.8931	$121.89	$121.90	$121.90
Purchase #2	$250.78	7.339%	$269.1847	$269.18	$269.20	$269.20
Purchase #3	$56.46	5.307%	$59.4563	$59.46	$59.45	$59.50
Purchase #4	$173.62	13.388%	$196.8642	$196.86	$196.85	$196.90
Purchase #5	$115.94	10.306%	$127.8888	$127.89	$127.90	$127.90
Purchase #6	$20.57	12.795%	$23.2019	$23.20	$23.20	$23.20
Purchase #7	$54.28	13.861%	$61.8038	$61.80	$61.80	$61.80
7 purchase totals =	$784.11		$860.2928	$860.28	$860.30	$860.40