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	$162.70	4.778%	$170.4738	$170.47	$170.45	$170.50
Purchase #2	$235.38	8.651%	$255.7427	$255.74	$255.75	$255.70
Purchase #3	$170.78	8.397%	$185.1204	$185.12	$185.10	$185.10
Purchase #4	$105.66	6.517%	$112.5459	$112.55	$112.55	$112.50
Purchase #5	$237.86	10.123%	$261.9386	$261.94	$261.95	$261.90
Purchase #6	$47.63	13.525%	$54.072	$54.07	$54.05	$54.10
Purchase #7	$44.72	9.276%	$48.8682	$48.87	$48.85	$48.90
7 purchase totals =	$1,004.73		$1,088.7616	$1,088.76	$1,088.70	$1,088.70