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	$143.90	4.397%	$150.2273	$150.23	$150.25	$150.20
Purchase #2	$138.44	10.180%	$152.5332	$152.53	$152.55	$152.50
Purchase #3	$111.78	6.797%	$119.3777	$119.38	$119.40	$119.40
Purchase #4	$208.54	9.751%	$228.8747	$228.87	$228.85	$228.90
Purchase #5	$156.86	12.465%	$176.4126	$176.41	$176.40	$176.40
Purchase #6	$99.64	7.323%	$106.9366	$106.94	$106.95	$106.90
Purchase #7	$38.99	11.596%	$43.5113	$43.51	$43.50	$43.50
7 purchase totals =	$898.15		$977.8734	$977.87	$977.90	$977.80