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	$156.80	13.559%	$178.0605	$178.06	$178.05	$178.10
Purchase #2	$28.34	4.515%	$29.6196	$29.62	$29.60	$29.60
Purchase #3	$220.59	8.310%	$238.921	$238.92	$238.90	$238.90
Purchase #4	$52.65	7.339%	$56.514	$56.51	$56.50	$56.50
Purchase #5	$65.64	12.386%	$73.7702	$73.77	$73.75	$73.80
Purchase #6	$186.75	7.228%	$200.2483	$200.25	$200.25	$200.20
Purchase #7	$19.39	7.217%	$20.7894	$20.79	$20.80	$20.80
7 purchase totals =	$730.16		$797.9230	$797.92	$797.85	$797.90