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	$77.40	6.540%	$82.462	$82.46	$82.45	$82.50
Purchase #2	$18.59	12.808%	$20.971	$20.97	$20.95	$21.00
Purchase #3	$151.52	10.597%	$167.5766	$167.58	$167.60	$167.60
Purchase #4	$28.99	5.815%	$30.6758	$30.68	$30.70	$30.70
Purchase #5	$104.72	4.330%	$109.2544	$109.25	$109.25	$109.30
Purchase #6	$230.87	9.618%	$253.0751	$253.08	$253.10	$253.10
Purchase #7	$243.35	5.558%	$256.8754	$256.88	$256.90	$256.90
7 purchase totals =	$855.44		$920.8903	$920.90	$920.95	$921.10