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	$24.25	12.468%	$27.2735	$27.27	$27.25	$27.30
Purchase #2	$148.74	10.626%	$164.5451	$164.55	$164.55	$164.50
Purchase #3	$146.37	6.341%	$155.6513	$155.65	$155.65	$155.70
Purchase #4	$106.82	5.378%	$112.5648	$112.56	$112.55	$112.60
Purchase #5	$200.57	6.772%	$214.1526	$214.15	$214.15	$214.20
Purchase #6	$118.82	6.186%	$126.1702	$126.17	$126.15	$126.20
Purchase #7	$37.82	12.631%	$42.597	$42.60	$42.60	$42.60
7 purchase totals =	$783.39		$842.9545	$842.95	$842.90	$843.10