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	$29.29	6.480%	$31.188	$31.19	$31.20	$31.20
Purchase #2	$171.90	3.788%	$178.4116	$178.41	$178.40	$178.40
Purchase #3	$246.44	13.102%	$278.7286	$278.73	$278.75	$278.70
Purchase #4	$151.58	8.242%	$164.0732	$164.07	$164.05	$164.10
Purchase #5	$157.58	4.339%	$164.4174	$164.42	$164.40	$164.40
Purchase #6	$51.85	4.302%	$54.0806	$54.08	$54.10	$54.10
Purchase #7	$211.59	12.846%	$238.7709	$238.77	$238.75	$238.80
7 purchase totals =	$1,020.23		$1,109.6703	$1,109.67	$1,109.65	$1,109.70