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	$75.57	12.351%	$84.9037	$84.90	$84.90	$84.90
Purchase #2	$233.58	3.462%	$241.6665	$241.67	$241.65	$241.70
Purchase #3	$19.55	5.406%	$20.6069	$20.61	$20.60	$20.60
Purchase #4	$116.27	13.760%	$132.2688	$132.27	$132.25	$132.30
Purchase #5	$99.34	11.860%	$111.1217	$111.12	$111.10	$111.10
Purchase #6	$196.76	5.872%	$208.3137	$208.31	$208.30	$208.30
Purchase #7	$59.40	5.335%	$62.569	$62.57	$62.55	$62.60
7 purchase totals =	$800.47		$861.4503	$861.45	$861.35	$861.50