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	$200.44	12.560%	$225.6153	$225.62	$225.60	$225.60
Purchase #2	$176.54	7.702%	$190.1371	$190.14	$190.15	$190.10
Purchase #3	$53.77	5.682%	$56.8252	$56.83	$56.85	$56.80
Purchase #4	$40.47	13.254%	$45.8339	$45.83	$45.85	$45.80
Purchase #5	$96.40	3.628%	$99.8974	$99.90	$99.90	$99.90
Purchase #6	$152.86	11.269%	$170.0858	$170.09	$170.10	$170.10
Purchase #7	$191.79	7.116%	$205.4378	$205.44	$205.45	$205.40
7 purchase totals =	$912.27		$993.8325	$993.85	$993.90	$993.70