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	$128.86	6.422%	$137.1354	$137.14	$137.15	$137.10
Purchase #2	$188.85	7.534%	$203.078	$203.08	$203.10	$203.10
Purchase #3	$74.64	9.351%	$81.6196	$81.62	$81.60	$81.60
Purchase #4	$124.69	4.596%	$130.4208	$130.42	$130.40	$130.40
Purchase #5	$40.41	6.163%	$42.9005	$42.90	$42.90	$42.90
Purchase #6	$49.34	7.228%	$52.9063	$52.91	$52.90	$52.90
Purchase #7	$37.71	6.328%	$40.0963	$40.10	$40.10	$40.10
7 purchase totals =	$644.50		$688.1569	$688.17	$688.15	$688.10