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	$109.53	13.774%	$124.6167	$124.62	$124.60	$124.60
Purchase #2	$38.82	8.540%	$42.1352	$42.14	$42.15	$42.10
Purchase #3	$38.87	3.235%	$40.1274	$40.13	$40.15	$40.10
Purchase #4	$168.86	12.205%	$189.4694	$189.47	$189.45	$189.50
Purchase #5	$247.53	9.255%	$270.4389	$270.44	$270.45	$270.40
Purchase #6	$127.72	10.319%	$140.8994	$140.90	$140.90	$140.90
Purchase #7	$146.28	6.643%	$155.9974	$156.00	$156.00	$156.00
7 purchase totals =	$877.61		$963.6844	$963.70	$963.70	$963.60