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	$111.76	13.448%	$126.7895	$126.79	$126.80	$126.80
Purchase #2	$45.77	9.262%	$50.0092	$50.01	$50.00	$50.00
Purchase #3	$155.90	7.720%	$167.9355	$167.94	$167.95	$167.90
Purchase #4	$103.94	7.178%	$111.4008	$111.40	$111.40	$111.40
Purchase #5	$121.25	3.504%	$125.4986	$125.50	$125.50	$125.50
Purchase #6	$107.77	9.539%	$118.0502	$118.05	$118.05	$118.10
Purchase #7	$88.86	10.288%	$98.0019	$98.00	$98.00	$98.00
7 purchase totals =	$735.25		$797.6857	$797.69	$797.70	$797.70