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	$169.80	3.836%	$176.3135	$176.31	$176.30	$176.30
Purchase #2	$63.25	13.355%	$71.697	$71.70	$71.70	$71.70
Purchase #3	$241.72	8.193%	$261.5241	$261.52	$261.50	$261.50
Purchase #4	$34.94	9.148%	$38.1363	$38.14	$38.15	$38.10
Purchase #5	$124.69	13.256%	$141.2189	$141.22	$141.20	$141.20
Purchase #6	$168.72	5.301%	$177.6638	$177.66	$177.65	$177.70
Purchase #7	$99.78	11.742%	$111.4962	$111.50	$111.50	$111.50
7 purchase totals =	$902.90		$978.0498	$978.05	$978.00	$978.00