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	$244.52	11.608%	$272.9039	$272.90	$272.90	$272.90
Purchase #2	$97.82	8.183%	$105.8246	$105.82	$105.80	$105.80
Purchase #3	$127.31	3.690%	$132.0077	$132.01	$132.00	$132.00
Purchase #4	$49.45	8.357%	$53.5825	$53.58	$53.60	$53.60
Purchase #5	$178.85	13.720%	$203.3882	$203.39	$203.40	$203.40
Purchase #6	$82.63	11.131%	$91.8275	$91.83	$91.85	$91.80
Purchase #7	$138.28	8.665%	$150.262	$150.26	$150.25	$150.30
7 purchase totals =	$918.86		$1,009.7964	$1,009.79	$1,009.80	$1,009.80