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	$14.39	13.266%	$16.299	$16.30	$16.30	$16.30
Purchase #2	$69.42	13.218%	$78.5959	$78.60	$78.60	$78.60
Purchase #3	$202.31	8.335%	$219.1725	$219.17	$219.15	$219.20
Purchase #4	$41.29	5.489%	$43.5564	$43.56	$43.55	$43.60
Purchase #5	$116.54	5.585%	$123.0488	$123.05	$123.05	$123.00
Purchase #6	$46.37	3.825%	$48.1437	$48.14	$48.15	$48.10
Purchase #7	$123.72	3.689%	$128.284	$128.28	$128.30	$128.30
7 purchase totals =	$614.04		$657.1003	$657.10	$657.10	$657.10