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	$44.75	10.269%	$49.3454	$49.35	$49.35	$49.30
Purchase #2	$41.90	3.671%	$43.4381	$43.44	$43.45	$43.40
Purchase #3	$208.44	9.758%	$228.7796	$228.78	$228.80	$228.80
Purchase #4	$233.45	3.167%	$240.8434	$240.84	$240.85	$240.80
Purchase #5	$131.43	13.794%	$149.5595	$149.56	$149.55	$149.60
Purchase #6	$65.45	3.301%	$67.6105	$67.61	$67.60	$67.60
Purchase #7	$79.25	13.149%	$89.6706	$89.67	$89.65	$89.70
7 purchase totals =	$804.67		$869.2471	$869.25	$869.25	$869.20