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	$47.39	9.493%	$51.8887	$51.89	$51.90	$51.90
Purchase #2	$36.70	7.453%	$39.4353	$39.44	$39.45	$39.40
Purchase #3	$73.60	4.700%	$77.0592	$77.06	$77.05	$77.10
Purchase #4	$54.53	11.823%	$60.9771	$60.98	$61.00	$61.00
Purchase #5	$64.31	6.244%	$68.3255	$68.33	$68.35	$68.30
Purchase #6	$19.37	13.450%	$21.9753	$21.98	$22.00	$22.00
Purchase #7	$56.28	6.390%	$59.8763	$59.88	$59.90	$59.90
7 purchase totals =	$352.18		$379.5374	$379.56	$379.65	$379.60