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	$155.70	10.260%	$171.6748	$171.67	$171.65	$171.70
Purchase #2	$35.71	13.499%	$40.5305	$40.53	$40.55	$40.50
Purchase #3	$236.45	7.673%	$254.5928	$254.59	$254.60	$254.60
Purchase #4	$151.33	9.565%	$165.8047	$165.80	$165.80	$165.80
Purchase #5	$11.83	10.728%	$13.0991	$13.10	$13.10	$13.10
Purchase #6	$77.98	3.682%	$80.8512	$80.85	$80.85	$80.90
Purchase #7	$50.47	8.418%	$54.7186	$54.72	$54.70	$54.70
7 purchase totals =	$719.47		$781.2717	$781.26	$781.25	$781.30