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	$13.36	12.757%	$15.0643	$15.06	$15.05	$15.10
Purchase #2	$244.88	13.555%	$278.0735	$278.07	$278.05	$278.10
Purchase #3	$66.68	7.716%	$71.825	$71.83	$71.85	$71.80
Purchase #4	$52.52	10.170%	$57.8613	$57.86	$57.85	$57.90
Purchase #5	$105.76	6.761%	$112.9104	$112.91	$112.90	$112.90
Purchase #6	$41.52	12.250%	$46.6062	$46.61	$46.60	$46.60
Purchase #7	$77.92	3.820%	$80.8965	$80.90	$80.90	$80.90
7 purchase totals =	$602.64		$663.2372	$663.24	$663.20	$663.30