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	$144.60	12.354%	$162.4639	$162.46	$162.45	$162.50
Purchase #2	$44.93	5.656%	$47.4712	$47.47	$47.45	$47.50
Purchase #3	$230.78	10.688%	$255.4458	$255.45	$255.45	$255.40
Purchase #4	$130.40	8.554%	$141.5544	$141.55	$141.55	$141.60
Purchase #5	$85.79	12.868%	$96.8295	$96.83	$96.85	$96.80
Purchase #6	$203.73	12.448%	$229.0903	$229.09	$229.10	$229.10
Purchase #7	$70.45	11.237%	$78.3665	$78.37	$78.35	$78.40
7 purchase totals =	$910.68		$1,011.2216	$1,011.22	$1,011.20	$1,011.30