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	$11.60	10.676%	$12.8384	$12.84	$12.85	$12.80
Purchase #2	$71.61	13.496%	$81.2745	$81.27	$81.25	$81.30
Purchase #3	$233.81	4.363%	$244.0111	$244.01	$244.00	$244.00
Purchase #4	$196.34	3.648%	$203.5025	$203.50	$203.50	$203.50
Purchase #5	$13.57	12.819%	$15.3095	$15.31	$15.30	$15.30
Purchase #6	$37.82	12.186%	$42.4287	$42.43	$42.45	$42.40
Purchase #7	$144.83	12.409%	$162.802	$162.80	$162.80	$162.80
7 purchase totals =	$709.58		$762.1667	$762.16	$762.15	$762.10