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	$26.81	3.326%	$27.7017	$27.70	$27.70	$27.70
Purchase #2	$167.44	3.601%	$173.4695	$173.47	$173.45	$173.50
Purchase #3	$19.58	9.403%	$21.4211	$21.42	$21.40	$21.40
Purchase #4	$126.44	12.705%	$142.5042	$142.50	$142.50	$142.50
Purchase #5	$67.79	5.233%	$71.3375	$71.34	$71.35	$71.30
Purchase #6	$150.88	10.187%	$166.2501	$166.25	$166.25	$166.30
Purchase #7	$74.95	9.586%	$82.1347	$82.13	$82.15	$82.10
7 purchase totals =	$633.89		$684.8188	$684.81	$684.80	$684.80