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	$229.46	12.175%	$257.3968	$257.40	$257.40	$257.40
Purchase #2	$36.54	11.762%	$40.8378	$40.84	$40.85	$40.80
Purchase #3	$216.28	6.146%	$229.5726	$229.57	$229.55	$229.60
Purchase #4	$45.51	6.486%	$48.4618	$48.46	$48.45	$48.50
Purchase #5	$40.88	13.205%	$46.2782	$46.28	$46.30	$46.30
Purchase #6	$92.47	6.784%	$98.7432	$98.74	$98.75	$98.70
Purchase #7	$233.52	9.763%	$256.3186	$256.32	$256.30	$256.30
7 purchase totals =	$894.66		$977.6090	$977.61	$977.60	$977.60