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	$37.59	7.805%	$40.5239	$40.52	$40.50	$40.50
Purchase #2	$217.38	8.229%	$235.2682	$235.27	$235.25	$235.30
Purchase #3	$37.60	5.847%	$39.7985	$39.80	$39.80	$39.80
Purchase #4	$234.94	11.277%	$261.4342	$261.43	$261.45	$261.40
Purchase #5	$45.53	10.735%	$50.4176	$50.42	$50.40	$50.40
Purchase #6	$103.62	12.770%	$116.8523	$116.85	$116.85	$116.90
Purchase #7	$113.85	11.417%	$126.8483	$126.85	$126.85	$126.80
7 purchase totals =	$790.51		$871.1430	$871.14	$871.10	$871.10