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	$114.41	8.532%	$124.1715	$124.17	$124.15	$124.20
Purchase #2	$124.50	4.584%	$130.2071	$130.21	$130.20	$130.20
Purchase #3	$51.49	7.839%	$55.5263	$55.53	$55.55	$55.50
Purchase #4	$204.69	9.147%	$223.413	$223.41	$223.40	$223.40
Purchase #5	$54.44	8.481%	$59.0571	$59.06	$59.05	$59.10
Purchase #6	$148.30	11.296%	$165.052	$165.05	$165.05	$165.10
Purchase #7	$210.86	10.536%	$233.0762	$233.08	$233.10	$233.10
7 purchase totals =	$908.69		$990.5032	$990.51	$990.50	$990.60