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	$123.30	11.371%	$137.3204	$137.32	$137.30	$137.30
Purchase #2	$153.95	11.512%	$171.6727	$171.67	$171.65	$171.70
Purchase #3	$54.27	12.395%	$60.9968	$61.00	$61.00	$61.00
Purchase #4	$160.31	4.208%	$167.0558	$167.06	$167.05	$167.10
Purchase #5	$236.84	10.370%	$261.4003	$261.40	$261.40	$261.40
Purchase #6	$60.31	5.231%	$63.4648	$63.46	$63.45	$63.50
Purchase #7	$206.90	12.740%	$233.2591	$233.26	$233.25	$233.30
7 purchase totals =	$995.88		$1,095.1699	$1,095.17	$1,095.10	$1,095.30