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	$89.91	11.691%	$100.4214	$100.42	$100.40	$100.40
Purchase #2	$100.79	6.490%	$107.3313	$107.33	$107.35	$107.30
Purchase #3	$238.28	9.255%	$260.3328	$260.33	$260.35	$260.30
Purchase #4	$124.77	6.463%	$132.8339	$132.83	$132.85	$132.80
Purchase #5	$128.89	6.656%	$137.4689	$137.47	$137.45	$137.50
Purchase #6	$125.94	4.159%	$131.1778	$131.18	$131.20	$131.20
Purchase #7	$37.91	12.742%	$42.7405	$42.74	$42.75	$42.70
7 purchase totals =	$846.49		$912.3066	$912.30	$912.35	$912.20