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	$240.56	12.135%	$269.752	$269.75	$269.75	$269.80
Purchase #2	$58.47	9.595%	$64.0802	$64.08	$64.10	$64.10
Purchase #3	$243.94	6.248%	$259.1814	$259.18	$259.20	$259.20
Purchase #4	$151.25	8.606%	$164.2666	$164.27	$164.25	$164.30
Purchase #5	$87.62	3.341%	$90.5474	$90.55	$90.55	$90.50
Purchase #6	$79.46	12.734%	$89.5784	$89.58	$89.60	$89.60
Purchase #7	$25.30	8.195%	$27.3733	$27.37	$27.35	$27.40
7 purchase totals =	$886.60		$964.7793	$964.78	$964.80	$964.90