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	$231.75	10.237%	$255.4742	$255.47	$255.45	$255.50
Purchase #2	$205.93	13.556%	$233.8459	$233.85	$233.85	$233.80
Purchase #3	$205.96	8.430%	$223.3224	$223.32	$223.30	$223.30
Purchase #4	$127.25	10.725%	$140.8976	$140.90	$140.90	$140.90
Purchase #5	$226.47	6.581%	$241.374	$241.37	$241.35	$241.40
Purchase #6	$38.30	9.380%	$41.8925	$41.89	$41.90	$41.90
Purchase #7	$134.83	4.143%	$140.416	$140.42	$140.40	$140.40
7 purchase totals =	$1,170.49		$1,277.2226	$1,277.22	$1,277.15	$1,277.20