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	$239.92	4.158%	$249.8959	$249.90	$249.90	$249.90
Purchase #2	$141.68	10.237%	$156.1838	$156.18	$156.20	$156.20
Purchase #3	$54.59	8.526%	$59.2443	$59.24	$59.25	$59.20
Purchase #4	$139.28	11.386%	$155.1384	$155.14	$155.15	$155.10
Purchase #5	$85.88	10.691%	$95.0614	$95.06	$95.05	$95.10
Purchase #6	$178.59	6.523%	$190.2394	$190.24	$190.25	$190.20
Purchase #7	$55.42	6.755%	$59.1636	$59.16	$59.15	$59.20
7 purchase totals =	$895.36		$964.9268	$964.92	$964.95	$964.90