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	$150.81	13.691%	$171.4574	$171.46	$171.45	$171.50
Purchase #2	$133.81	6.256%	$142.1812	$142.18	$142.20	$142.20
Purchase #3	$116.53	10.243%	$128.4662	$128.47	$128.45	$128.50
Purchase #4	$25.96	5.787%	$27.4623	$27.46	$27.45	$27.50
Purchase #5	$230.92	9.742%	$253.4162	$253.42	$253.40	$253.40
Purchase #6	$70.37	13.135%	$79.6131	$79.61	$79.60	$79.60
Purchase #7	$50.41	7.358%	$54.1192	$54.12	$54.10	$54.10
7 purchase totals =	$778.81		$856.7156	$856.72	$856.65	$856.80