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	$48.65	5.320%	$51.2382	$51.24	$51.25	$51.20
Purchase #2	$53.51	4.200%	$55.7574	$55.76	$55.75	$55.80
Purchase #3	$56.89	13.850%	$64.7693	$64.77	$64.75	$64.80
Purchase #4	$131.31	11.219%	$146.0417	$146.04	$146.05	$146.00
Purchase #5	$135.41	9.804%	$148.6856	$148.69	$148.70	$148.70
Purchase #6	$28.74	3.785%	$29.8278	$29.83	$29.85	$29.80
Purchase #7	$34.42	7.771%	$37.0948	$37.09	$37.10	$37.10
7 purchase totals =	$488.93		$533.4148	$533.42	$533.45	$533.40