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	$40.90	11.591%	$45.6407	$45.64	$45.65	$45.60
Purchase #2	$65.60	10.573%	$72.5359	$72.54	$72.55	$72.50
Purchase #3	$233.32	13.554%	$264.9442	$264.94	$264.95	$264.90
Purchase #4	$86.80	12.393%	$97.5571	$97.56	$97.55	$97.60
Purchase #5	$46.36	3.526%	$47.9947	$47.99	$48.00	$48.00
Purchase #6	$95.52	9.693%	$104.7788	$104.78	$104.80	$104.80
Purchase #7	$169.45	4.120%	$176.4313	$176.43	$176.45	$176.40
7 purchase totals =	$737.95		$809.8827	$809.88	$809.95	$809.80