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	$54.48	9.302%	$59.5477	$59.55	$59.55	$59.50
Purchase #2	$50.55	3.581%	$52.3602	$52.36	$52.35	$52.40
Purchase #3	$221.89	12.159%	$248.8696	$248.87	$248.85	$248.90
Purchase #4	$87.65	10.571%	$96.9155	$96.92	$96.90	$96.90
Purchase #5	$134.65	7.612%	$144.8996	$144.90	$144.90	$144.90
Purchase #6	$57.52	7.669%	$61.9312	$61.93	$61.95	$61.90
Purchase #7	$126.25	4.781%	$132.286	$132.29	$132.30	$132.30
7 purchase totals =	$732.99		$796.8098	$796.82	$796.80	$796.80