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	$232.51	5.153%	$244.4912	$244.49	$244.50	$244.50
Purchase #2	$142.50	9.348%	$155.8209	$155.82	$155.80	$155.80
Purchase #3	$114.52	4.223%	$119.3562	$119.36	$119.35	$119.40
Purchase #4	$33.47	6.160%	$35.5318	$35.53	$35.55	$35.50
Purchase #5	$215.53	9.409%	$235.8092	$235.81	$235.80	$235.80
Purchase #6	$79.43	13.605%	$90.2365	$90.24	$90.25	$90.20
Purchase #7	$98.39	5.301%	$103.6057	$103.61	$103.60	$103.60
7 purchase totals =	$916.35		$984.8515	$984.86	$984.85	$984.80