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	$23.76	3.166%	$24.5122	$24.51	$24.50	$24.50
Purchase #2	$128.68	10.195%	$141.7989	$141.80	$141.80	$141.80
Purchase #3	$193.37	11.663%	$215.9227	$215.92	$215.90	$215.90
Purchase #4	$199.28	3.685%	$206.6235	$206.62	$206.60	$206.60
Purchase #5	$178.28	5.193%	$187.5381	$187.54	$187.55	$187.50
Purchase #6	$129.50	9.517%	$141.8245	$141.82	$141.80	$141.80
Purchase #7	$118.43	8.832%	$128.8897	$128.89	$128.90	$128.90
7 purchase totals =	$971.30		$1,047.1096	$1,047.10	$1,047.05	$1,047.00