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	$86.32	3.735%	$89.5441	$89.54	$89.55	$89.50
Purchase #2	$36.53	5.257%	$38.4504	$38.45	$38.45	$38.50
Purchase #3	$34.32	9.674%	$37.6401	$37.64	$37.65	$37.60
Purchase #4	$15.70	10.357%	$17.326	$17.33	$17.35	$17.30
Purchase #5	$107.56	6.506%	$114.5579	$114.56	$114.55	$114.60
Purchase #6	$89.37	12.657%	$100.6816	$100.68	$100.70	$100.70
Purchase #7	$31.38	9.408%	$34.3322	$34.33	$34.35	$34.30
7 purchase totals =	$401.18		$432.5323	$432.53	$432.60	$432.50