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	$227.88	5.226%	$239.789	$239.79	$239.80	$239.80
Purchase #2	$204.89	9.617%	$224.5943	$224.59	$224.60	$224.60
Purchase #3	$53.75	6.280%	$57.1255	$57.13	$57.15	$57.10
Purchase #4	$174.34	12.486%	$196.1081	$196.11	$196.10	$196.10
Purchase #5	$42.39	8.491%	$45.9893	$45.99	$46.00	$46.00
Purchase #6	$17.81	9.284%	$19.4635	$19.46	$19.45	$19.50
Purchase #7	$11.88	13.499%	$13.4837	$13.48	$13.50	$13.50
7 purchase totals =	$732.94		$796.5534	$796.55	$796.60	$796.60