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	$60.38	10.405%	$66.6625	$66.66	$66.65	$66.70
Purchase #2	$40.28	8.411%	$43.668	$43.67	$43.65	$43.70
Purchase #3	$212.44	13.541%	$241.2065	$241.21	$241.20	$241.20
Purchase #4	$114.29	3.567%	$118.3667	$118.37	$118.35	$118.40
Purchase #5	$194.58	13.798%	$221.4281	$221.43	$221.45	$221.40
Purchase #6	$238.37	12.125%	$267.2724	$267.27	$267.25	$267.30
Purchase #7	$53.65	10.624%	$59.3498	$59.35	$59.35	$59.30
7 purchase totals =	$913.99		$1,017.9540	$1,017.96	$1,017.90	$1,018.00