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	$143.76	7.756%	$154.91	$154.91	$154.90	$154.90
Purchase #2	$118.25	8.141%	$127.8767	$127.88	$127.90	$127.90
Purchase #3	$140.61	13.218%	$159.1958	$159.20	$159.20	$159.20
Purchase #4	$37.88	8.487%	$41.0949	$41.09	$41.10	$41.10
Purchase #5	$68.70	5.598%	$72.5458	$72.55	$72.55	$72.50
Purchase #6	$237.28	3.211%	$244.8991	$244.90	$244.90	$244.90
Purchase #7	$248.33	12.608%	$279.6394	$279.64	$279.65	$279.60
7 purchase totals =	$994.81		$1,080.1617	$1,080.17	$1,080.20	$1,080.10