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	$115.59	6.839%	$123.4952	$123.50	$123.50	$123.50
Purchase #2	$16.53	10.168%	$18.2108	$18.21	$18.20	$18.20
Purchase #3	$237.89	9.329%	$260.0828	$260.08	$260.10	$260.10
Purchase #4	$122.83	6.262%	$130.5216	$130.52	$130.50	$130.50
Purchase #5	$105.43	7.732%	$113.5818	$113.58	$113.60	$113.60
Purchase #6	$42.55	6.771%	$45.4311	$45.43	$45.45	$45.40
Purchase #7	$78.41	13.106%	$88.6864	$88.69	$88.70	$88.70
7 purchase totals =	$719.23		$780.0097	$780.01	$780.05	$780.00