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	$70.80	13.468%	$80.3353	$80.34	$80.35	$80.30
Purchase #2	$177.50	12.322%	$199.3716	$199.37	$199.35	$199.40
Purchase #3	$115.96	10.242%	$127.8366	$127.84	$127.85	$127.80
Purchase #4	$226.47	9.247%	$247.4117	$247.41	$247.40	$247.40
Purchase #5	$74.53	10.556%	$82.3974	$82.40	$82.40	$82.40
Purchase #6	$52.92	12.174%	$59.3625	$59.36	$59.35	$59.40
Purchase #7	$57.56	13.557%	$65.3634	$65.36	$65.35	$65.40
7 purchase totals =	$775.74		$862.0785	$862.08	$862.05	$862.10