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	$148.30	12.322%	$166.5735	$166.57	$166.55	$166.60
Purchase #2	$130.34	8.480%	$141.3928	$141.39	$141.40	$141.40
Purchase #3	$244.28	4.749%	$255.8809	$255.88	$255.90	$255.90
Purchase #4	$99.86	12.557%	$112.3994	$112.40	$112.40	$112.40
Purchase #5	$107.80	9.528%	$118.0712	$118.07	$118.05	$118.10
Purchase #6	$233.63	6.364%	$248.4982	$248.50	$248.50	$248.50
Purchase #7	$158.73	9.270%	$173.4443	$173.44	$173.45	$173.40
7 purchase totals =	$1,122.94		$1,216.2603	$1,216.25	$1,216.25	$1,216.30