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	$29.46	12.803%	$33.2318	$33.23	$33.25	$33.20
Purchase #2	$175.63	9.102%	$191.6158	$191.62	$191.60	$191.60
Purchase #3	$172.32	10.293%	$190.0569	$190.06	$190.05	$190.10
Purchase #4	$126.95	10.227%	$139.9332	$139.93	$139.95	$139.90
Purchase #5	$84.25	4.846%	$88.3328	$88.33	$88.35	$88.30
Purchase #6	$155.52	13.727%	$176.8682	$176.87	$176.85	$176.90
Purchase #7	$52.27	13.764%	$59.4644	$59.46	$59.45	$59.50
7 purchase totals =	$796.40		$879.5031	$879.50	$879.50	$879.50