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	$98.88	12.800%	$111.5366	$111.54	$111.55	$111.50
Purchase #2	$141.85	13.313%	$160.7345	$160.73	$160.75	$160.70
Purchase #3	$83.82	7.628%	$90.2138	$90.21	$90.20	$90.20
Purchase #4	$133.31	6.569%	$142.0671	$142.07	$142.05	$142.10
Purchase #5	$226.68	9.597%	$248.4345	$248.43	$248.45	$248.40
Purchase #6	$69.52	13.177%	$78.6807	$78.68	$78.70	$78.70
Purchase #7	$238.27	13.491%	$270.415	$270.42	$270.40	$270.40
7 purchase totals =	$992.33		$1,102.0822	$1,102.08	$1,102.10	$1,102.00