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	$80.71	10.138%	$88.8924	$88.89	$88.90	$88.90
Purchase #2	$115.88	6.593%	$123.52	$123.52	$123.50	$123.50
Purchase #3	$146.51	10.636%	$162.0928	$162.09	$162.10	$162.10
Purchase #4	$73.68	3.622%	$76.3487	$76.35	$76.35	$76.30
Purchase #5	$71.41	5.434%	$75.2904	$75.29	$75.30	$75.30
Purchase #6	$173.48	10.259%	$191.2773	$191.28	$191.30	$191.30
Purchase #7	$242.76	8.505%	$263.4067	$263.41	$263.40	$263.40
7 purchase totals =	$904.43		$980.8283	$980.83	$980.85	$980.80