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	$13.33	3.527%	$13.8001	$13.80	$13.80	$13.80
Purchase #2	$174.54	7.331%	$187.3355	$187.34	$187.35	$187.30
Purchase #3	$119.45	3.368%	$123.4731	$123.47	$123.45	$123.50
Purchase #4	$18.25	7.381%	$19.597	$19.60	$19.60	$19.60
Purchase #5	$9.55	11.592%	$10.657	$10.66	$10.65	$10.70
Purchase #6	$11.67	10.409%	$12.8847	$12.88	$12.90	$12.90
Purchase #7	$50.64	13.301%	$57.3756	$57.38	$57.40	$57.40
7 purchase totals =	$397.43		$425.1230	$425.13	$425.15	$425.20