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	$33.33	13.218%	$37.7356	$37.74	$37.75	$37.70
Purchase #2	$213.66	8.152%	$231.0776	$231.08	$231.10	$231.10
Purchase #3	$126.75	4.348%	$132.2611	$132.26	$132.25	$132.30
Purchase #4	$117.65	8.522%	$127.6761	$127.68	$127.70	$127.70
Purchase #5	$109.38	3.746%	$113.4774	$113.48	$113.50	$113.50
Purchase #6	$127.44	3.312%	$131.6608	$131.66	$131.65	$131.70
Purchase #7	$49.33	10.247%	$54.3848	$54.38	$54.40	$54.40
7 purchase totals =	$777.54		$828.2734	$828.28	$828.35	$828.40