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	$249.55	11.541%	$278.3506	$278.35	$278.35	$278.40
Purchase #2	$105.84	13.155%	$119.7633	$119.76	$119.75	$119.80
Purchase #3	$139.51	13.505%	$158.3508	$158.35	$158.35	$158.40
Purchase #4	$108.32	3.457%	$112.0646	$112.06	$112.05	$112.10
Purchase #5	$162.50	3.329%	$167.9096	$167.91	$167.90	$167.90
Purchase #6	$246.78	10.228%	$272.0207	$272.02	$272.00	$272.00
Purchase #7	$9.56	9.217%	$10.4411	$10.44	$10.45	$10.40
7 purchase totals =	$1,022.06		$1,118.9007	$1,118.89	$1,118.85	$1,119.00