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	$200.69	8.752%	$218.2544	$218.25	$218.25	$218.30
Purchase #2	$52.52	12.793%	$59.2389	$59.24	$59.25	$59.20
Purchase #3	$126.81	9.748%	$139.1714	$139.17	$139.15	$139.20
Purchase #4	$100.88	8.164%	$109.1158	$109.12	$109.10	$109.10
Purchase #5	$37.96	12.429%	$42.678	$42.68	$42.70	$42.70
Purchase #6	$14.78	5.291%	$15.562	$15.56	$15.55	$15.60
Purchase #7	$115.92	8.836%	$126.1627	$126.16	$126.15	$126.20
7 purchase totals =	$649.56		$710.1832	$710.18	$710.15	$710.30