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	$113.41	12.383%	$127.4536	$127.45	$127.45	$127.50
Purchase #2	$88.84	6.824%	$94.9024	$94.90	$94.90	$94.90
Purchase #3	$69.27	7.528%	$74.4846	$74.48	$74.50	$74.50
Purchase #4	$145.60	12.681%	$164.0635	$164.06	$164.05	$164.10
Purchase #5	$148.82	6.753%	$158.8698	$158.87	$158.85	$158.90
Purchase #6	$30.54	3.227%	$31.5255	$31.53	$31.55	$31.50
Purchase #7	$71.88	5.161%	$75.5897	$75.59	$75.60	$75.60
7 purchase totals =	$668.36		$726.8891	$726.88	$726.90	$727.00