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	$26.68	3.558%	$27.6293	$27.63	$27.65	$27.60
Purchase #2	$155.84	12.600%	$175.4758	$175.48	$175.50	$175.50
Purchase #3	$82.49	10.168%	$90.8776	$90.88	$90.90	$90.90
Purchase #4	$155.55	7.660%	$167.4651	$167.47	$167.45	$167.50
Purchase #5	$134.62	12.608%	$151.5929	$151.59	$151.60	$151.60
Purchase #6	$179.35	9.425%	$196.2537	$196.25	$196.25	$196.30
Purchase #7	$164.55	4.307%	$171.6372	$171.64	$171.65	$171.60
7 purchase totals =	$899.08		$980.9316	$980.94	$981.00	$981.00