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	$179.25	3.174%	$184.9394	$184.94	$184.95	$184.90
Purchase #2	$68.92	4.497%	$72.0193	$72.02	$72.00	$72.00
Purchase #3	$158.31	8.265%	$171.3943	$171.39	$171.40	$171.40
Purchase #4	$59.26	5.456%	$62.4932	$62.49	$62.50	$62.50
Purchase #5	$181.39	9.283%	$198.2284	$198.23	$198.25	$198.20
Purchase #6	$197.38	13.131%	$223.298	$223.30	$223.30	$223.30
Purchase #7	$66.99	7.748%	$72.1804	$72.18	$72.20	$72.20
7 purchase totals =	$911.50		$984.5530	$984.55	$984.60	$984.50