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	$99.72	6.190%	$105.8927	$105.89	$105.90	$105.90
Purchase #2	$90.97	5.289%	$95.7814	$95.78	$95.80	$95.80
Purchase #3	$29.48	5.763%	$31.1789	$31.18	$31.20	$31.20
Purchase #4	$127.40	4.447%	$133.0655	$133.07	$133.05	$133.10
Purchase #5	$154.93	13.263%	$175.4784	$175.48	$175.50	$175.50
Purchase #6	$37.60	11.341%	$41.8642	$41.86	$41.85	$41.90
Purchase #7	$51.86	10.775%	$57.4479	$57.45	$57.45	$57.40
7 purchase totals =	$591.96		$640.7090	$640.71	$640.75	$640.80