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	$24.78	11.183%	$27.5511	$27.55	$27.55	$27.60
Purchase #2	$14.58	4.499%	$15.236	$15.24	$15.25	$15.20
Purchase #3	$81.91	9.313%	$89.5383	$89.54	$89.55	$89.50
Purchase #4	$239.90	3.480%	$248.2485	$248.25	$248.25	$248.20
Purchase #5	$48.42	8.763%	$52.663	$52.66	$52.65	$52.70
Purchase #6	$160.42	13.310%	$181.7719	$181.77	$181.75	$181.80
Purchase #7	$113.90	11.729%	$127.2593	$127.26	$127.25	$127.30
7 purchase totals =	$683.91		$742.2681	$742.27	$742.25	$742.30