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	$103.39	8.745%	$112.4315	$112.43	$112.45	$112.40
Purchase #2	$196.71	12.743%	$221.7768	$221.78	$221.80	$221.80
Purchase #3	$224.77	12.157%	$252.0953	$252.10	$252.10	$252.10
Purchase #4	$100.25	5.243%	$105.5061	$105.51	$105.50	$105.50
Purchase #5	$144.40	11.820%	$161.4681	$161.47	$161.45	$161.50
Purchase #6	$42.27	9.586%	$46.322	$46.32	$46.30	$46.30
Purchase #7	$219.93	10.167%	$242.2903	$242.29	$242.30	$242.30
7 purchase totals =	$1,031.72		$1,141.8901	$1,141.90	$1,141.90	$1,141.90