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	$89.39	12.484%	$100.5494	$100.55	$100.55	$100.50
Purchase #2	$24.31	13.859%	$27.6791	$27.68	$27.70	$27.70
Purchase #3	$106.32	11.269%	$118.3012	$118.30	$118.30	$118.30
Purchase #4	$246.85	9.741%	$270.8957	$270.90	$270.90	$270.90
Purchase #5	$30.37	13.280%	$34.4031	$34.40	$34.40	$34.40
Purchase #6	$146.29	8.136%	$158.1922	$158.19	$158.20	$158.20
Purchase #7	$53.56	4.595%	$56.0211	$56.02	$56.00	$56.00
7 purchase totals =	$697.09		$766.0418	$766.04	$766.05	$766.00