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	$71.27	4.321%	$74.3496	$74.35	$74.35	$74.30
Purchase #2	$158.88	3.551%	$164.5218	$164.52	$164.50	$164.50
Purchase #3	$43.41	4.238%	$45.2497	$45.25	$45.25	$45.20
Purchase #4	$233.45	5.324%	$245.8789	$245.88	$245.90	$245.90
Purchase #5	$46.75	6.715%	$49.8893	$49.89	$49.90	$49.90
Purchase #6	$18.47	12.837%	$20.841	$20.84	$20.85	$20.80
Purchase #7	$188.86	13.681%	$214.6979	$214.70	$214.70	$214.70
7 purchase totals =	$761.09		$815.4282	$815.43	$815.45	$815.30