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	$128.85	13.743%	$146.5579	$146.56	$146.55	$146.60
Purchase #2	$71.64	9.750%	$78.6249	$78.62	$78.60	$78.60
Purchase #3	$179.70	5.634%	$189.8243	$189.82	$189.80	$189.80
Purchase #4	$101.54	9.649%	$111.3376	$111.34	$111.35	$111.30
Purchase #5	$97.53	5.792%	$103.1789	$103.18	$103.20	$103.20
Purchase #6	$23.32	11.192%	$25.93	$25.93	$25.95	$25.90
Purchase #7	$151.98	7.820%	$163.8648	$163.86	$163.85	$163.90
7 purchase totals =	$754.56		$819.3184	$819.31	$819.30	$819.30