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	$205.39	12.169%	$230.3839	$230.38	$230.40	$230.40
Purchase #2	$75.96	13.617%	$86.3035	$86.30	$86.30	$86.30
Purchase #3	$84.92	5.866%	$89.9014	$89.90	$89.90	$89.90
Purchase #4	$25.35	9.549%	$27.7707	$27.77	$27.75	$27.80
Purchase #5	$19.29	4.742%	$20.2047	$20.20	$20.20	$20.20
Purchase #6	$159.81	3.270%	$165.0358	$165.04	$165.05	$165.00
Purchase #7	$150.74	11.837%	$168.5831	$168.58	$168.60	$168.60
7 purchase totals =	$721.46		$788.1831	$788.17	$788.20	$788.20