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	$131.60	5.575%	$138.9367	$138.94	$138.95	$138.90
Purchase #2	$24.25	7.211%	$25.9987	$26.00	$26.00	$26.00
Purchase #3	$234.35	4.240%	$244.2864	$244.29	$244.30	$244.30
Purchase #4	$192.47	3.182%	$198.5944	$198.59	$198.60	$198.60
Purchase #5	$49.94	6.592%	$53.232	$53.23	$53.25	$53.20
Purchase #6	$162.46	4.643%	$170.003	$170.00	$170.00	$170.00
Purchase #7	$89.86	11.796%	$100.4599	$100.46	$100.45	$100.50
7 purchase totals =	$884.93		$931.5111	$931.51	$931.55	$931.50