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	$49.81	9.187%	$54.386	$54.39	$54.40	$54.40
Purchase #2	$30.46	3.706%	$31.5888	$31.59	$31.60	$31.60
Purchase #3	$19.33	13.232%	$21.8877	$21.89	$21.90	$21.90
Purchase #4	$168.80	9.845%	$185.4184	$185.42	$185.40	$185.40
Purchase #5	$168.32	10.436%	$185.8859	$185.89	$185.90	$185.90
Purchase #6	$141.68	4.401%	$147.9153	$147.92	$147.90	$147.90
Purchase #7	$167.82	9.627%	$183.976	$183.98	$184.00	$184.00
7 purchase totals =	$746.22		$811.0581	$811.08	$811.10	$811.10