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	$175.39	3.546%	$181.6093	$181.61	$181.60	$181.60
Purchase #2	$105.29	5.668%	$111.2578	$111.26	$111.25	$111.30
Purchase #3	$156.93	10.294%	$173.0844	$173.08	$173.10	$173.10
Purchase #4	$159.94	9.102%	$174.4977	$174.50	$174.50	$174.50
Purchase #5	$128.77	8.719%	$139.9975	$140.00	$140.00	$140.00
Purchase #6	$23.77	3.516%	$24.6058	$24.61	$24.60	$24.60
Purchase #7	$89.61	9.253%	$97.9016	$97.90	$97.90	$97.90
7 purchase totals =	$839.70		$902.9541	$902.96	$902.95	$903.00