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	$151.87	11.719%	$169.6676	$169.67	$169.65	$169.70
Purchase #2	$173.71	10.153%	$191.3468	$191.35	$191.35	$191.30
Purchase #3	$105.40	10.348%	$116.3068	$116.31	$116.30	$116.30
Purchase #4	$37.81	12.469%	$42.5245	$42.52	$42.50	$42.50
Purchase #5	$43.60	7.834%	$47.0156	$47.02	$47.00	$47.00
Purchase #6	$114.64	13.597%	$130.2276	$130.23	$130.25	$130.20
Purchase #7	$215.71	8.631%	$234.3279	$234.33	$234.35	$234.30
7 purchase totals =	$842.74		$931.4168	$931.43	$931.40	$931.30