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	$210.86	12.624%	$237.479	$237.48	$237.50	$237.50
Purchase #2	$153.84	9.446%	$168.3717	$168.37	$168.35	$168.40
Purchase #3	$145.31	7.242%	$155.8334	$155.83	$155.85	$155.80
Purchase #4	$151.62	4.215%	$158.0108	$158.01	$158.00	$158.00
Purchase #5	$19.53	12.140%	$21.9009	$21.90	$21.90	$21.90
Purchase #6	$156.25	9.692%	$171.3938	$171.39	$171.40	$171.40
Purchase #7	$70.72	8.377%	$76.6442	$76.64	$76.65	$76.60
7 purchase totals =	$908.13		$989.6338	$989.62	$989.65	$989.60