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	$37.64	6.347%	$40.029	$40.03	$40.05	$40.00
Purchase #2	$57.40	8.250%	$62.1355	$62.14	$62.15	$62.10
Purchase #3	$237.47	7.827%	$256.0568	$256.06	$256.05	$256.10
Purchase #4	$186.89	5.220%	$196.6457	$196.65	$196.65	$196.60
Purchase #5	$41.53	9.193%	$45.3479	$45.35	$45.35	$45.30
Purchase #6	$76.80	3.862%	$79.766	$79.77	$79.75	$79.80
Purchase #7	$11.77	7.117%	$12.6077	$12.61	$12.60	$12.60
7 purchase totals =	$649.50		$692.5886	$692.61	$692.60	$692.50