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	$78.38	12.274%	$88.0004	$88.00	$88.00	$88.00
Purchase #2	$46.54	13.529%	$52.8364	$52.84	$52.85	$52.80
Purchase #3	$250.90	7.249%	$269.0877	$269.09	$269.10	$269.10
Purchase #4	$198.37	9.688%	$217.5881	$217.59	$217.60	$217.60
Purchase #5	$152.60	7.749%	$164.425	$164.43	$164.45	$164.40
Purchase #6	$16.31	7.847%	$17.5898	$17.59	$17.60	$17.60
Purchase #7	$106.28	4.451%	$111.0105	$111.01	$111.00	$111.00
7 purchase totals =	$849.38		$920.5379	$920.55	$920.60	$920.50