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	$21.86	13.534%	$24.8185	$24.82	$24.80	$24.80
Purchase #2	$77.64	12.319%	$87.2045	$87.20	$87.20	$87.20
Purchase #3	$68.57	4.115%	$71.3917	$71.39	$71.40	$71.40
Purchase #4	$147.42	10.469%	$162.8534	$162.85	$162.85	$162.90
Purchase #5	$203.89	7.136%	$218.4396	$218.44	$218.45	$218.40
Purchase #6	$45.57	12.202%	$51.1305	$51.13	$51.15	$51.10
Purchase #7	$233.77	9.395%	$255.7327	$255.73	$255.75	$255.70
7 purchase totals =	$798.72		$871.5709	$871.56	$871.60	$871.50