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	$126.55	8.501%	$137.308	$137.31	$137.30	$137.30
Purchase #2	$160.35	4.660%	$167.8223	$167.82	$167.80	$167.80
Purchase #3	$78.76	9.178%	$85.9886	$85.99	$86.00	$86.00
Purchase #4	$200.61	7.112%	$214.8774	$214.88	$214.90	$214.90
Purchase #5	$22.85	13.241%	$25.8756	$25.88	$25.90	$25.90
Purchase #6	$171.26	4.312%	$178.6447	$178.64	$178.65	$178.60
Purchase #7	$28.78	10.845%	$31.9012	$31.90	$31.90	$31.90
7 purchase totals =	$789.16		$842.4178	$842.42	$842.45	$842.40