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	$43.59	7.574%	$46.8915	$46.89	$46.90	$46.90
Purchase #2	$234.49	10.637%	$259.4327	$259.43	$259.45	$259.40
Purchase #3	$161.33	3.625%	$167.1782	$167.18	$167.20	$167.20
Purchase #4	$138.86	10.541%	$153.4972	$153.50	$153.50	$153.50
Purchase #5	$42.96	10.280%	$47.3763	$47.38	$47.40	$47.40
Purchase #6	$34.89	10.858%	$38.6784	$38.68	$38.70	$38.70
Purchase #7	$54.83	13.784%	$62.3878	$62.39	$62.40	$62.40
7 purchase totals =	$710.95		$775.4421	$775.45	$775.55	$775.50