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	$21.39	9.582%	$23.4396	$23.44	$23.45	$23.40
Purchase #2	$138.84	6.287%	$147.5689	$147.57	$147.55	$147.60
Purchase #3	$240.45	7.554%	$258.6136	$258.61	$258.60	$258.60
Purchase #4	$101.31	5.532%	$106.9145	$106.91	$106.90	$106.90
Purchase #5	$54.60	8.508%	$59.2454	$59.25	$59.25	$59.20
Purchase #6	$156.95	10.163%	$172.9008	$172.90	$172.90	$172.90
Purchase #7	$82.45	9.720%	$90.4641	$90.46	$90.45	$90.50
7 purchase totals =	$795.99		$859.1469	$859.14	$859.10	$859.10