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	$20.96	4.461%	$21.895	$21.90	$21.90	$21.90
Purchase #2	$200.83	13.701%	$228.3457	$228.35	$228.35	$228.30
Purchase #3	$54.26	6.493%	$57.7831	$57.78	$57.80	$57.80
Purchase #4	$193.97	13.704%	$220.5516	$220.55	$220.55	$220.60
Purchase #5	$48.78	11.801%	$54.5365	$54.54	$54.55	$54.50
Purchase #6	$185.87	4.657%	$194.526	$194.53	$194.55	$194.50
Purchase #7	$59.65	11.621%	$66.5819	$66.58	$66.60	$66.60
7 purchase totals =	$764.32		$844.2198	$844.23	$844.30	$844.20