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	$180.91	4.536%	$189.1161	$189.12	$189.10	$189.10
Purchase #2	$233.60	11.605%	$260.7093	$260.71	$260.70	$260.70
Purchase #3	$179.63	4.174%	$187.1278	$187.13	$187.15	$187.10
Purchase #4	$77.56	5.822%	$82.0755	$82.08	$82.10	$82.10
Purchase #5	$89.78	11.489%	$100.0948	$100.09	$100.10	$100.10
Purchase #6	$151.99	6.533%	$161.9195	$161.92	$161.90	$161.90
Purchase #7	$171.83	7.418%	$184.5763	$184.58	$184.60	$184.60
7 purchase totals =	$1,085.30		$1,165.6193	$1,165.63	$1,165.65	$1,165.60