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	$36.68	10.401%	$40.4951	$40.50	$40.50	$40.50
Purchase #2	$47.40	13.208%	$53.6606	$53.66	$53.65	$53.70
Purchase #3	$72.34	11.765%	$80.8508	$80.85	$80.85	$80.90
Purchase #4	$135.85	13.243%	$153.8406	$153.84	$153.85	$153.80
Purchase #5	$28.60	10.604%	$31.6327	$31.63	$31.65	$31.60
Purchase #6	$16.39	7.533%	$17.6247	$17.62	$17.60	$17.60
Purchase #7	$112.68	13.153%	$127.5008	$127.50	$127.50	$127.50
7 purchase totals =	$449.94		$505.6053	$505.60	$505.60	$505.60