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	$96.38	13.394%	$109.2891	$109.29	$109.30	$109.30
Purchase #2	$139.67	4.155%	$145.4733	$145.47	$145.45	$145.50
Purchase #3	$11.76	4.534%	$12.2932	$12.29	$12.30	$12.30
Purchase #4	$90.31	8.390%	$97.887	$97.89	$97.90	$97.90
Purchase #5	$216.39	10.399%	$238.8924	$238.89	$238.90	$238.90
Purchase #6	$249.72	6.716%	$266.4912	$266.49	$266.50	$266.50
Purchase #7	$123.88	12.525%	$139.396	$139.40	$139.40	$139.40
7 purchase totals =	$928.11		$1,009.7222	$1,009.72	$1,009.75	$1,009.80