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	$230.42	12.137%	$258.3861	$258.39	$258.40	$258.40
Purchase #2	$54.50	12.496%	$61.3103	$61.31	$61.30	$61.30
Purchase #3	$40.82	6.149%	$43.33	$43.33	$43.35	$43.30
Purchase #4	$13.47	3.854%	$13.9891	$13.99	$14.00	$14.00
Purchase #5	$170.52	4.570%	$178.3128	$178.31	$178.30	$178.30
Purchase #6	$124.59	5.630%	$131.6044	$131.60	$131.60	$131.60
Purchase #7	$77.53	10.164%	$85.4101	$85.41	$85.40	$85.40
7 purchase totals =	$711.85		$772.3428	$772.34	$772.35	$772.30