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	$49.78	8.521%	$54.0218	$54.02	$54.00	$54.00
Purchase #2	$151.91	10.112%	$167.2711	$167.27	$167.25	$167.30
Purchase #3	$143.75	7.639%	$154.7311	$154.73	$154.75	$154.70
Purchase #4	$24.38	12.740%	$27.486	$27.49	$27.50	$27.50
Purchase #5	$204.88	7.527%	$220.3013	$220.30	$220.30	$220.30
Purchase #6	$222.89	4.728%	$233.4282	$233.43	$233.45	$233.40
Purchase #7	$222.54	7.797%	$239.8914	$239.89	$239.90	$239.90
7 purchase totals =	$1,020.13		$1,097.1309	$1,097.13	$1,097.15	$1,097.10