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	$138.28	12.160%	$155.0948	$155.09	$155.10	$155.10
Purchase #2	$82.37	7.160%	$88.2677	$88.27	$88.25	$88.30
Purchase #3	$130.84	10.515%	$144.5978	$144.60	$144.60	$144.60
Purchase #4	$213.30	7.670%	$229.6601	$229.66	$229.65	$229.70
Purchase #5	$69.92	9.548%	$76.596	$76.60	$76.60	$76.60
Purchase #6	$212.78	12.270%	$238.8881	$238.89	$238.90	$238.90
Purchase #7	$145.75	13.393%	$165.2703	$165.27	$165.25	$165.30
7 purchase totals =	$993.24		$1,098.3748	$1,098.38	$1,098.35	$1,098.50