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	$17.70	6.377%	$18.8287	$18.83	$18.85	$18.80
Purchase #2	$192.42	10.358%	$212.3509	$212.35	$212.35	$212.40
Purchase #3	$147.48	6.172%	$156.5825	$156.58	$156.60	$156.60
Purchase #4	$107.77	3.762%	$111.8243	$111.82	$111.80	$111.80
Purchase #5	$146.60	12.146%	$164.406	$164.41	$164.40	$164.40
Purchase #6	$85.60	12.105%	$95.9619	$95.96	$95.95	$96.00
Purchase #7	$234.36	10.145%	$258.1358	$258.14	$258.15	$258.10
7 purchase totals =	$931.93		$1,018.0901	$1,018.09	$1,018.10	$1,018.10