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	$170.70	8.649%	$185.4638	$185.46	$185.45	$185.50
Purchase #2	$128.98	10.247%	$142.1966	$142.20	$142.20	$142.20
Purchase #3	$238.44	5.728%	$252.0978	$252.10	$252.10	$252.10
Purchase #4	$141.58	11.777%	$158.2539	$158.25	$158.25	$158.30
Purchase #5	$98.33	13.619%	$111.7216	$111.72	$111.70	$111.70
Purchase #6	$106.56	4.610%	$111.4724	$111.47	$111.45	$111.50
Purchase #7	$121.52	3.432%	$125.6906	$125.69	$125.70	$125.70
7 purchase totals =	$1,006.11		$1,086.8967	$1,086.89	$1,086.85	$1,087.00