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	$109.57	12.793%	$123.5873	$123.59	$123.60	$123.60
Purchase #2	$114.52	3.677%	$118.7309	$118.73	$118.75	$118.70
Purchase #3	$54.94	13.844%	$62.5459	$62.55	$62.55	$62.50
Purchase #4	$60.61	6.274%	$64.4127	$64.41	$64.40	$64.40
Purchase #5	$55.35	3.750%	$57.4256	$57.43	$57.45	$57.40
Purchase #6	$61.71	12.772%	$69.5916	$69.59	$69.60	$69.60
Purchase #7	$248.78	4.729%	$260.5448	$260.54	$260.55	$260.50
7 purchase totals =	$705.48		$756.8388	$756.84	$756.90	$756.70