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	$40.25	5.381%	$42.4159	$42.42	$42.40	$42.40
Purchase #2	$87.70	9.760%	$96.2595	$96.26	$96.25	$96.30
Purchase #3	$109.89	4.165%	$114.4669	$114.47	$114.45	$114.50
Purchase #4	$69.96	10.593%	$77.3709	$77.37	$77.35	$77.40
Purchase #5	$215.75	13.279%	$244.3994	$244.40	$244.40	$244.40
Purchase #6	$20.30	4.550%	$21.2237	$21.22	$21.20	$21.20
Purchase #7	$214.58	7.260%	$230.1585	$230.16	$230.15	$230.20
7 purchase totals =	$758.43		$826.2948	$826.30	$826.20	$826.40