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	$56.50	5.351%	$59.5233	$59.52	$59.50	$59.50
Purchase #2	$227.42	5.847%	$240.7172	$240.72	$240.70	$240.70
Purchase #3	$102.25	9.402%	$111.8635	$111.86	$111.85	$111.90
Purchase #4	$17.64	10.175%	$19.4349	$19.43	$19.45	$19.40
Purchase #5	$167.39	3.351%	$172.9992	$173.00	$173.00	$173.00
Purchase #6	$49.69	7.673%	$53.5027	$53.50	$53.50	$53.50
Purchase #7	$202.35	9.836%	$222.2531	$222.25	$222.25	$222.30
7 purchase totals =	$823.24		$880.2939	$880.28	$880.25	$880.30