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	$82.28	5.241%	$86.5923	$86.59	$86.60	$86.60
Purchase #2	$195.66	12.560%	$220.2349	$220.23	$220.25	$220.20
Purchase #3	$177.47	5.456%	$187.1528	$187.15	$187.15	$187.20
Purchase #4	$12.25	12.505%	$13.7819	$13.78	$13.80	$13.80
Purchase #5	$238.78	8.241%	$258.4579	$258.46	$258.45	$258.50
Purchase #6	$81.38	8.861%	$88.5911	$88.59	$88.60	$88.60
Purchase #7	$60.71	11.629%	$67.77	$67.77	$67.75	$67.80
7 purchase totals =	$848.53		$922.5809	$922.57	$922.60	$922.70