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	$186.25	13.191%	$210.8182	$210.82	$210.80	$210.80
Purchase #2	$131.64	5.131%	$138.3944	$138.39	$138.40	$138.40
Purchase #3	$48.60	10.240%	$53.5766	$53.58	$53.60	$53.60
Purchase #4	$131.77	4.286%	$137.4177	$137.42	$137.40	$137.40
Purchase #5	$31.51	6.443%	$33.5402	$33.54	$33.55	$33.50
Purchase #6	$184.46	8.448%	$200.0432	$200.04	$200.05	$200.00
Purchase #7	$123.34	6.518%	$131.3793	$131.38	$131.40	$131.40
7 purchase totals =	$837.57		$905.1696	$905.17	$905.20	$905.10