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	$49.80	12.633%	$56.0912	$56.09	$56.10	$56.10
Purchase #2	$50.59	5.342%	$53.2925	$53.29	$53.30	$53.30
Purchase #3	$40.28	13.789%	$45.8342	$45.83	$45.85	$45.80
Purchase #4	$96.58	9.209%	$105.4741	$105.47	$105.45	$105.50
Purchase #5	$186.43	13.800%	$212.1573	$212.16	$212.15	$212.20
Purchase #6	$219.39	10.506%	$242.4391	$242.44	$242.45	$242.40
Purchase #7	$167.28	9.384%	$182.9776	$182.98	$183.00	$183.00
7 purchase totals =	$810.35		$898.2660	$898.26	$898.30	$898.30