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	$248.39	6.403%	$264.2944	$264.29	$264.30	$264.30
Purchase #2	$217.96	12.402%	$244.9914	$244.99	$245.00	$245.00
Purchase #3	$231.40	6.321%	$246.0268	$246.03	$246.05	$246.00
Purchase #4	$238.61	7.237%	$255.8782	$255.88	$255.90	$255.90
Purchase #5	$100.30	11.562%	$111.8967	$111.90	$111.90	$111.90
Purchase #6	$78.99	5.440%	$83.2871	$83.29	$83.30	$83.30
Purchase #7	$43.33	4.178%	$45.1403	$45.14	$45.15	$45.10
7 purchase totals =	$1,158.98		$1,251.5149	$1,251.52	$1,251.60	$1,251.50