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	$90.79	13.747%	$103.2709	$103.27	$103.25	$103.30
Purchase #2	$71.75	6.649%	$76.5207	$76.52	$76.50	$76.50
Purchase #3	$157.69	6.252%	$167.5488	$167.55	$167.55	$167.50
Purchase #4	$94.32	12.252%	$105.8761	$105.88	$105.90	$105.90
Purchase #5	$220.28	7.412%	$236.6072	$236.61	$236.60	$236.60
Purchase #6	$226.78	6.658%	$241.879	$241.88	$241.90	$241.90
Purchase #7	$28.41	8.503%	$30.8257	$30.83	$30.85	$30.80
7 purchase totals =	$890.02		$962.5284	$962.54	$962.55	$962.50