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	$240.99	12.176%	$270.3329	$270.33	$270.35	$270.30
Purchase #2	$48.69	11.134%	$54.1111	$54.11	$54.10	$54.10
Purchase #3	$191.28	3.746%	$198.4453	$198.45	$198.45	$198.40
Purchase #4	$78.85	3.463%	$81.5806	$81.58	$81.60	$81.60
Purchase #5	$199.47	9.390%	$218.2002	$218.20	$218.20	$218.20
Purchase #6	$98.54	6.103%	$104.5539	$104.55	$104.55	$104.60
Purchase #7	$153.47	12.499%	$172.6522	$172.65	$172.65	$172.70
7 purchase totals =	$1,011.29		$1,099.8762	$1,099.87	$1,099.90	$1,099.90