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	$99.32	12.635%	$111.8691	$111.87	$111.85	$111.90
Purchase #2	$155.58	4.326%	$162.3104	$162.31	$162.30	$162.30
Purchase #3	$29.46	9.136%	$32.1515	$32.15	$32.15	$32.20
Purchase #4	$34.48	13.225%	$39.04	$39.04	$39.05	$39.00
Purchase #5	$43.79	12.272%	$49.1639	$49.16	$49.15	$49.20
Purchase #6	$138.40	3.537%	$143.2952	$143.30	$143.30	$143.30
Purchase #7	$52.94	5.526%	$55.8655	$55.87	$55.85	$55.90
7 purchase totals =	$553.97		$593.6956	$593.70	$593.65	$593.80