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	$43.89	9.547%	$48.0802	$48.08	$48.10	$48.10
Purchase #2	$249.74	8.476%	$270.908	$270.91	$270.90	$270.90
Purchase #3	$172.47	11.676%	$192.6076	$192.61	$192.60	$192.60
Purchase #4	$48.81	3.322%	$50.4315	$50.43	$50.45	$50.40
Purchase #5	$133.32	8.248%	$144.3162	$144.32	$144.30	$144.30
Purchase #6	$233.89	13.816%	$266.2042	$266.20	$266.20	$266.20
Purchase #7	$5.94	5.293%	$6.2544	$6.25	$6.25	$6.30
7 purchase totals =	$888.06		$978.8021	$978.80	$978.80	$978.80