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	$226.84	12.653%	$255.5421	$255.54	$255.55	$255.50
Purchase #2	$103.77	10.461%	$114.6254	$114.63	$114.65	$114.60
Purchase #3	$32.45	12.115%	$36.3813	$36.38	$36.40	$36.40
Purchase #4	$158.38	11.688%	$176.8915	$176.89	$176.90	$176.90
Purchase #5	$135.86	10.610%	$150.2747	$150.27	$150.25	$150.30
Purchase #6	$9.76	11.561%	$10.8884	$10.89	$10.90	$10.90
Purchase #7	$187.32	9.577%	$205.2596	$205.26	$205.25	$205.30
7 purchase totals =	$854.38		$949.8630	$949.86	$949.90	$949.90