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	$69.55	3.816%	$72.204	$72.20	$72.20	$72.20
Purchase #2	$158.62	12.498%	$178.4443	$178.44	$178.45	$178.40
Purchase #3	$163.91	13.413%	$185.8952	$185.90	$185.90	$185.90
Purchase #4	$127.98	8.590%	$138.9735	$138.97	$138.95	$139.00
Purchase #5	$131.97	5.812%	$139.6401	$139.64	$139.65	$139.60
Purchase #6	$136.94	4.560%	$143.1845	$143.18	$143.20	$143.20
Purchase #7	$101.62	9.377%	$111.1489	$111.15	$111.15	$111.10
7 purchase totals =	$890.59		$969.4905	$969.48	$969.50	$969.40