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	$163.57	13.383%	$185.4606	$185.46	$185.45	$185.50
Purchase #2	$144.35	4.338%	$150.6119	$150.61	$150.60	$150.60
Purchase #3	$121.45	4.554%	$126.9808	$126.98	$127.00	$127.00
Purchase #4	$115.93	10.523%	$128.1293	$128.13	$128.15	$128.10
Purchase #5	$64.34	10.511%	$71.1028	$71.10	$71.10	$71.10
Purchase #6	$25.58	6.164%	$27.1568	$27.16	$27.15	$27.20
Purchase #7	$137.57	9.668%	$150.8703	$150.87	$150.85	$150.90
7 purchase totals =	$772.79		$840.3125	$840.31	$840.30	$840.40