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	$55.70	9.655%	$61.0778	$61.08	$61.10	$61.10
Purchase #2	$138.77	4.645%	$145.2159	$145.22	$145.20	$145.20
Purchase #3	$61.32	10.434%	$67.7181	$67.72	$67.70	$67.70
Purchase #4	$46.73	5.395%	$49.2511	$49.25	$49.25	$49.30
Purchase #5	$126.42	12.404%	$142.1011	$142.10	$142.10	$142.10
Purchase #6	$140.59	3.476%	$145.4769	$145.48	$145.50	$145.50
Purchase #7	$113.47	5.697%	$119.9344	$119.93	$119.95	$119.90
7 purchase totals =	$683.00		$730.7753	$730.78	$730.80	$730.80