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	$159.32	12.502%	$179.2382	$179.24	$179.25	$179.20
Purchase #2	$128.43	6.191%	$136.3811	$136.38	$136.40	$136.40
Purchase #3	$13.43	9.392%	$14.6913	$14.69	$14.70	$14.70
Purchase #4	$241.90	5.680%	$255.6399	$255.64	$255.65	$255.60
Purchase #5	$72.91	10.521%	$80.5809	$80.58	$80.60	$80.60
Purchase #6	$102.85	7.568%	$110.6337	$110.63	$110.65	$110.60
Purchase #7	$38.93	11.250%	$43.3096	$43.31	$43.30	$43.30
7 purchase totals =	$757.77		$820.4747	$820.47	$820.55	$820.40