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	$190.38	13.261%	$215.6263	$215.63	$215.65	$215.60
Purchase #2	$52.57	3.719%	$54.5251	$54.53	$54.55	$54.50
Purchase #3	$186.38	10.138%	$205.2752	$205.28	$205.30	$205.30
Purchase #4	$100.89	10.341%	$111.323	$111.32	$111.30	$111.30
Purchase #5	$36.79	3.849%	$38.206	$38.21	$38.20	$38.20
Purchase #6	$162.71	5.321%	$171.3678	$171.37	$171.35	$171.40
Purchase #7	$41.57	3.800%	$43.1497	$43.15	$43.15	$43.10
7 purchase totals =	$771.29		$839.4731	$839.49	$839.50	$839.40