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	$99.29	4.704%	$103.9606	$103.96	$103.95	$104.00
Purchase #2	$37.35	12.858%	$42.1525	$42.15	$42.15	$42.20
Purchase #3	$135.63	13.277%	$153.6376	$153.64	$153.65	$153.60
Purchase #4	$13.83	7.131%	$14.8162	$14.82	$14.80	$14.80
Purchase #5	$78.41	10.349%	$86.5247	$86.52	$86.50	$86.50
Purchase #6	$64.28	11.757%	$71.8374	$71.84	$71.85	$71.80
Purchase #7	$104.49	13.120%	$118.1991	$118.20	$118.20	$118.20
7 purchase totals =	$533.28		$591.1281	$591.13	$591.10	$591.10