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	$18.51	5.870%	$19.5965	$19.60	$19.60	$19.60
Purchase #2	$102.53	8.139%	$110.8749	$110.87	$110.85	$110.90
Purchase #3	$185.94	13.255%	$210.5863	$210.59	$210.60	$210.60
Purchase #4	$153.43	3.308%	$158.5055	$158.51	$158.50	$158.50
Purchase #5	$203.37	12.177%	$228.1344	$228.13	$228.15	$228.10
Purchase #6	$141.71	10.588%	$156.7143	$156.71	$156.70	$156.70
Purchase #7	$69.55	13.446%	$78.9017	$78.90	$78.90	$78.90
7 purchase totals =	$875.04		$963.3136	$963.31	$963.30	$963.30