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	$12.61	9.326%	$13.786	$13.79	$13.80	$13.80
Purchase #2	$59.50	5.287%	$62.6458	$62.65	$62.65	$62.60
Purchase #3	$43.35	4.695%	$45.3853	$45.39	$45.40	$45.40
Purchase #4	$107.37	4.665%	$112.3788	$112.38	$112.40	$112.40
Purchase #5	$154.50	10.709%	$171.0454	$171.05	$171.05	$171.00
Purchase #6	$145.32	5.723%	$153.6367	$153.64	$153.65	$153.60
Purchase #7	$76.37	7.430%	$82.0443	$82.04	$82.05	$82.00
7 purchase totals =	$599.02		$640.9223	$640.94	$641.00	$640.80