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	$107.78	6.850%	$115.1629	$115.16	$115.15	$115.20
Purchase #2	$217.31	13.611%	$246.8881	$246.89	$246.90	$246.90
Purchase #3	$185.64	10.393%	$204.9336	$204.93	$204.95	$204.90
Purchase #4	$236.27	11.485%	$263.4056	$263.41	$263.40	$263.40
Purchase #5	$75.84	3.246%	$78.3018	$78.30	$78.30	$78.30
Purchase #6	$142.76	12.426%	$160.4994	$160.50	$160.50	$160.50
Purchase #7	$49.68	9.864%	$54.5804	$54.58	$54.60	$54.60
7 purchase totals =	$1,015.28		$1,123.7718	$1,123.77	$1,123.80	$1,123.80