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	$136.77	13.642%	$155.4282	$155.43	$155.45	$155.40
Purchase #2	$123.98	10.853%	$137.4355	$137.44	$137.45	$137.40
Purchase #3	$84.80	3.306%	$87.6035	$87.60	$87.60	$87.60
Purchase #4	$100.76	13.348%	$114.2094	$114.21	$114.20	$114.20
Purchase #5	$96.26	9.740%	$105.6357	$105.64	$105.65	$105.60
Purchase #6	$106.85	4.209%	$111.3473	$111.35	$111.35	$111.30
Purchase #7	$225.86	3.603%	$233.9977	$234.00	$234.00	$234.00
7 purchase totals =	$875.28		$945.6573	$945.67	$945.70	$945.50