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	$26.83	6.601%	$28.601	$28.60	$28.60	$28.60
Purchase #2	$100.79	4.339%	$105.1633	$105.16	$105.15	$105.20
Purchase #3	$182.88	7.424%	$196.457	$196.46	$196.45	$196.50
Purchase #4	$47.51	13.255%	$53.8075	$53.81	$53.80	$53.80
Purchase #5	$178.28	12.135%	$199.9143	$199.91	$199.90	$199.90
Purchase #6	$60.25	6.556%	$64.2	$64.20	$64.20	$64.20
Purchase #7	$75.77	7.490%	$81.4452	$81.45	$81.45	$81.40
7 purchase totals =	$672.31		$729.5883	$729.59	$729.55	$729.60