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	$240.52	12.106%	$269.6374	$269.64	$269.65	$269.60
Purchase #2	$97.32	6.592%	$103.7353	$103.74	$103.75	$103.70
Purchase #3	$60.96	13.635%	$69.2719	$69.27	$69.25	$69.30
Purchase #4	$73.27	10.112%	$80.6791	$80.68	$80.70	$80.70
Purchase #5	$34.86	11.189%	$38.7605	$38.76	$38.75	$38.80
Purchase #6	$89.42	11.839%	$100.0064	$100.01	$100.00	$100.00
Purchase #7	$7.29	4.480%	$7.6166	$7.62	$7.60	$7.60
7 purchase totals =	$603.64		$669.7072	$669.72	$669.70	$669.70