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	$123.61	6.767%	$131.9747	$131.97	$131.95	$132.00
Purchase #2	$21.88	12.446%	$24.6032	$24.60	$24.60	$24.60
Purchase #3	$185.50	13.291%	$210.1548	$210.15	$210.15	$210.20
Purchase #4	$141.78	12.704%	$159.7917	$159.79	$159.80	$159.80
Purchase #5	$231.45	7.621%	$249.0888	$249.09	$249.10	$249.10
Purchase #6	$65.90	4.377%	$68.7844	$68.78	$68.80	$68.80
Purchase #7	$246.71	3.776%	$256.0258	$256.03	$256.05	$256.00
7 purchase totals =	$1,016.83		$1,100.4234	$1,100.41	$1,100.45	$1,100.50