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	$10.39	10.528%	$11.4839	$11.48	$11.50	$11.50
Purchase #2	$178.42	7.767%	$192.2779	$192.28	$192.30	$192.30
Purchase #3	$60.83	6.645%	$64.8722	$64.87	$64.85	$64.90
Purchase #4	$212.92	13.813%	$242.3306	$242.33	$242.35	$242.30
Purchase #5	$33.82	12.693%	$38.1128	$38.11	$38.10	$38.10
Purchase #6	$152.98	9.188%	$167.0358	$167.04	$167.05	$167.00
Purchase #7	$241.54	8.244%	$261.4526	$261.45	$261.45	$261.50
7 purchase totals =	$890.90		$977.5658	$977.56	$977.60	$977.60