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	$119.84	3.325%	$123.8247	$123.82	$123.80	$123.80
Purchase #2	$234.35	3.460%	$242.4585	$242.46	$242.45	$242.50
Purchase #3	$13.28	13.218%	$15.0354	$15.04	$15.05	$15.00
Purchase #4	$123.26	13.519%	$139.9235	$139.92	$139.90	$139.90
Purchase #5	$139.62	11.278%	$155.3663	$155.37	$155.35	$155.40
Purchase #6	$139.52	9.139%	$152.2707	$152.27	$152.25	$152.30
Purchase #7	$111.80	5.539%	$117.9926	$117.99	$118.00	$118.00
7 purchase totals =	$881.67		$946.8717	$946.87	$946.80	$946.90