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	$230.26	4.359%	$240.297	$240.30	$240.30	$240.30
Purchase #2	$128.79	9.697%	$141.2788	$141.28	$141.30	$141.30
Purchase #3	$44.72	6.313%	$47.5432	$47.54	$47.55	$47.50
Purchase #4	$172.97	13.366%	$196.0892	$196.09	$196.10	$196.10
Purchase #5	$114.51	11.690%	$127.8962	$127.90	$127.90	$127.90
Purchase #6	$180.35	9.721%	$197.8818	$197.88	$197.90	$197.90
Purchase #7	$127.81	8.729%	$138.9665	$138.97	$138.95	$139.00
7 purchase totals =	$999.41		$1,089.9527	$1,089.96	$1,090.00	$1,090.00