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	$59.51	11.369%	$66.2757	$66.28	$66.30	$66.30
Purchase #2	$18.79	8.306%	$20.3507	$20.35	$20.35	$20.40
Purchase #3	$19.77	3.541%	$20.4701	$20.47	$20.45	$20.50
Purchase #4	$129.93	5.395%	$136.9397	$136.94	$136.95	$136.90
Purchase #5	$58.94	4.858%	$61.8033	$61.80	$61.80	$61.80
Purchase #6	$201.47	12.459%	$226.5711	$226.57	$226.55	$226.60
Purchase #7	$55.28	6.848%	$59.0656	$59.07	$59.05	$59.10
7 purchase totals =	$543.69		$591.4762	$591.48	$591.45	$591.60