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	$127.90	8.841%	$139.2076	$139.21	$139.20	$139.20
Purchase #2	$101.29	11.103%	$112.5362	$112.54	$112.55	$112.50
Purchase #3	$158.59	3.719%	$164.488	$164.49	$164.50	$164.50
Purchase #4	$153.50	3.458%	$158.808	$158.81	$158.80	$158.80
Purchase #5	$44.90	3.557%	$46.4971	$46.50	$46.50	$46.50
Purchase #6	$96.52	8.471%	$104.6962	$104.70	$104.70	$104.70
Purchase #7	$203.64	6.496%	$216.8685	$216.87	$216.85	$216.90
7 purchase totals =	$886.34		$943.1016	$943.12	$943.10	$943.10