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	$165.52	10.609%	$183.08	$183.08	$183.10	$183.10
Purchase #2	$93.46	11.389%	$104.1042	$104.10	$104.10	$104.10
Purchase #3	$53.91	4.600%	$56.3899	$56.39	$56.40	$56.40
Purchase #4	$131.66	9.335%	$143.9505	$143.95	$143.95	$144.00
Purchase #5	$75.50	4.240%	$78.7012	$78.70	$78.70	$78.70
Purchase #6	$171.69	11.418%	$191.2936	$191.29	$191.30	$191.30
Purchase #7	$132.77	9.491%	$145.3712	$145.37	$145.35	$145.40
7 purchase totals =	$824.51		$902.8906	$902.88	$902.90	$903.00