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	$34.49	12.260%	$38.7185	$38.72	$38.70	$38.70
Purchase #2	$56.88	4.771%	$59.5937	$59.59	$59.60	$59.60
Purchase #3	$109.58	13.214%	$124.0599	$124.06	$124.05	$124.10
Purchase #4	$144.34	6.150%	$153.2169	$153.22	$153.20	$153.20
Purchase #5	$150.37	13.247%	$170.2895	$170.29	$170.30	$170.30
Purchase #6	$84.38	7.303%	$90.5423	$90.54	$90.55	$90.50
Purchase #7	$63.92	13.322%	$72.4354	$72.44	$72.45	$72.40
7 purchase totals =	$643.96		$708.8562	$708.86	$708.85	$708.80