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	$91.83	13.267%	$104.0131	$104.01	$104.00	$104.00
Purchase #2	$136.77	11.523%	$152.53	$152.53	$152.55	$152.50
Purchase #3	$215.37	10.548%	$238.0872	$238.09	$238.10	$238.10
Purchase #4	$131.45	5.758%	$139.0189	$139.02	$139.00	$139.00
Purchase #5	$9.48	5.663%	$10.0169	$10.02	$10.00	$10.00
Purchase #6	$204.81	5.439%	$215.9496	$215.95	$215.95	$215.90
Purchase #7	$56.69	10.784%	$62.8034	$62.80	$62.80	$62.80
7 purchase totals =	$846.40		$922.4191	$922.42	$922.40	$922.30