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	$206.31	4.844%	$216.3037	$216.30	$216.30	$216.30
Purchase #2	$47.52	10.619%	$52.5661	$52.57	$52.55	$52.60
Purchase #3	$79.50	4.194%	$82.8342	$82.83	$82.85	$82.80
Purchase #4	$214.34	9.198%	$234.055	$234.06	$234.05	$234.10
Purchase #5	$156.85	13.786%	$178.4733	$178.47	$178.45	$178.50
Purchase #6	$244.44	5.665%	$258.2875	$258.29	$258.30	$258.30
Purchase #7	$66.27	3.106%	$68.3283	$68.33	$68.35	$68.30
7 purchase totals =	$1,015.23		$1,090.8481	$1,090.85	$1,090.85	$1,090.90