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	$111.95	4.856%	$117.3863	$117.39	$117.40	$117.40
Purchase #2	$193.31	9.606%	$211.8794	$211.88	$211.90	$211.90
Purchase #3	$175.80	6.869%	$187.8757	$187.88	$187.90	$187.90
Purchase #4	$62.29	9.810%	$68.4006	$68.40	$68.40	$68.40
Purchase #5	$105.77	5.255%	$111.3282	$111.33	$111.35	$111.30
Purchase #6	$59.40	6.315%	$63.1511	$63.15	$63.15	$63.20
Purchase #7	$213.73	7.363%	$229.4669	$229.47	$229.45	$229.50
7 purchase totals =	$922.25		$989.4882	$989.50	$989.55	$989.60