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	$241.32	3.793%	$250.4733	$250.47	$250.45	$250.50
Purchase #2	$138.86	5.732%	$146.8195	$146.82	$146.80	$146.80
Purchase #3	$165.62	10.211%	$182.5315	$182.53	$182.55	$182.50
Purchase #4	$99.91	8.649%	$108.5512	$108.55	$108.55	$108.60
Purchase #5	$85.60	13.384%	$97.0567	$97.06	$97.05	$97.10
Purchase #6	$36.98	7.756%	$39.8482	$39.85	$39.85	$39.80
Purchase #7	$241.96	6.314%	$257.2374	$257.24	$257.25	$257.20
7 purchase totals =	$1,010.25		$1,082.5178	$1,082.52	$1,082.50	$1,082.50