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	$135.45	5.790%	$143.2926	$143.29	$143.30	$143.30
Purchase #2	$37.89	8.102%	$40.9598	$40.96	$40.95	$41.00
Purchase #3	$120.83	6.337%	$128.487	$128.49	$128.50	$128.50
Purchase #4	$30.27	4.592%	$31.66	$31.66	$31.65	$31.70
Purchase #5	$228.27	12.563%	$256.9476	$256.95	$256.95	$256.90
Purchase #6	$101.51	9.608%	$111.2631	$111.26	$111.25	$111.30
Purchase #7	$43.67	6.591%	$46.5483	$46.55	$46.55	$46.50
7 purchase totals =	$697.89		$759.1584	$759.16	$759.15	$759.20