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	$10.94	12.747%	$12.3345	$12.33	$12.35	$12.30
Purchase #2	$119.94	12.191%	$134.5619	$134.56	$134.55	$134.60
Purchase #3	$162.79	10.136%	$179.2904	$179.29	$179.30	$179.30
Purchase #4	$250.84	8.584%	$272.3721	$272.37	$272.35	$272.40
Purchase #5	$142.94	5.136%	$150.2814	$150.28	$150.30	$150.30
Purchase #6	$39.25	7.451%	$42.1745	$42.17	$42.15	$42.20
Purchase #7	$16.82	10.560%	$18.5962	$18.60	$18.60	$18.60
7 purchase totals =	$743.52		$809.6110	$809.60	$809.60	$809.70