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	$246.91	3.784%	$256.2531	$256.25	$256.25	$256.30
Purchase #2	$183.82	13.778%	$209.1467	$209.15	$209.15	$209.10
Purchase #3	$154.98	11.675%	$173.0739	$173.07	$173.05	$173.10
Purchase #4	$101.44	7.839%	$109.3919	$109.39	$109.40	$109.40
Purchase #5	$245.98	3.374%	$254.2794	$254.28	$254.30	$254.30
Purchase #6	$41.52	10.120%	$45.7218	$45.72	$45.70	$45.70
Purchase #7	$65.75	9.595%	$72.0587	$72.06	$72.05	$72.10
7 purchase totals =	$1,040.40		$1,119.9255	$1,119.92	$1,119.90	$1,120.00