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	$159.46	8.807%	$173.5036	$173.50	$173.50	$173.50
Purchase #2	$140.52	8.557%	$152.5443	$152.54	$152.55	$152.50
Purchase #3	$14.26	13.786%	$16.2259	$16.23	$16.25	$16.20
Purchase #4	$39.26	10.631%	$43.4337	$43.43	$43.45	$43.40
Purchase #5	$43.43	12.640%	$48.9196	$48.92	$48.90	$48.90
Purchase #6	$57.48	11.842%	$64.2868	$64.29	$64.30	$64.30
Purchase #7	$125.40	4.836%	$131.4643	$131.46	$131.45	$131.50
7 purchase totals =	$579.81		$630.3782	$630.37	$630.40	$630.30