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	$172.52	6.493%	$183.7217	$183.72	$183.70	$183.70
Purchase #2	$69.41	12.727%	$78.2438	$78.24	$78.25	$78.20
Purchase #3	$236.78	9.597%	$259.5038	$259.50	$259.50	$259.50
Purchase #4	$153.72	13.871%	$175.0425	$175.04	$175.05	$175.00
Purchase #5	$22.69	7.554%	$24.404	$24.40	$24.40	$24.40
Purchase #6	$132.92	5.745%	$140.5563	$140.56	$140.55	$140.60
Purchase #7	$78.63	4.739%	$82.3563	$82.36	$82.35	$82.40
7 purchase totals =	$866.67		$943.8284	$943.82	$943.80	$943.80