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	$37.67	8.488%	$40.8674	$40.87	$40.85	$40.90
Purchase #2	$52.76	3.381%	$54.5438	$54.54	$54.55	$54.50
Purchase #3	$228.88	11.806%	$255.9016	$255.90	$255.90	$255.90
Purchase #4	$60.94	8.543%	$66.1461	$66.15	$66.15	$66.10
Purchase #5	$49.58	7.219%	$53.1592	$53.16	$53.15	$53.20
Purchase #6	$103.89	11.129%	$115.4519	$115.45	$115.45	$115.50
Purchase #7	$156.63	8.163%	$169.4157	$169.42	$169.40	$169.40
7 purchase totals =	$690.35		$755.4857	$755.49	$755.45	$755.50