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	$155.71	9.506%	$170.5118	$170.51	$170.50	$170.50
Purchase #2	$122.87	5.860%	$130.0702	$130.07	$130.05	$130.10
Purchase #3	$108.95	6.700%	$116.2497	$116.25	$116.25	$116.20
Purchase #4	$136.61	11.201%	$151.9117	$151.91	$151.90	$151.90
Purchase #5	$106.45	11.738%	$118.9451	$118.95	$118.95	$118.90
Purchase #6	$245.46	10.442%	$271.0909	$271.09	$271.10	$271.10
Purchase #7	$37.82	6.406%	$40.2427	$40.24	$40.25	$40.20
7 purchase totals =	$913.87		$999.0221	$999.02	$999.00	$998.90