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	$17.78	13.356%	$20.1547	$20.15	$20.15	$20.20
Purchase #2	$109.46	13.107%	$123.8069	$123.81	$123.80	$123.80
Purchase #3	$62.37	3.247%	$64.3952	$64.40	$64.40	$64.40
Purchase #4	$190.64	5.166%	$200.4885	$200.49	$200.50	$200.50
Purchase #5	$209.85	12.171%	$235.3908	$235.39	$235.40	$235.40
Purchase #6	$175.81	5.713%	$185.854	$185.85	$185.85	$185.90
Purchase #7	$74.70	9.566%	$81.8458	$81.85	$81.85	$81.80
7 purchase totals =	$840.61		$911.9359	$911.94	$911.95	$912.00