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	$162.69	12.669%	$183.3012	$183.30	$183.30	$183.30
Purchase #2	$107.29	5.757%	$113.4667	$113.47	$113.45	$113.50
Purchase #3	$168.93	12.714%	$190.4078	$190.41	$190.40	$190.40
Purchase #4	$14.46	10.391%	$15.9625	$15.96	$15.95	$16.00
Purchase #5	$70.78	3.137%	$73.0004	$73.00	$73.00	$73.00
Purchase #6	$92.31	7.356%	$99.1003	$99.10	$99.10	$99.10
Purchase #7	$12.25	13.497%	$13.9034	$13.90	$13.90	$13.90
7 purchase totals =	$628.71		$689.1423	$689.14	$689.10	$689.20