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	$174.54	7.353%	$187.3739	$187.37	$187.35	$187.40
Purchase #2	$208.90	5.231%	$219.8276	$219.83	$219.85	$219.80
Purchase #3	$179.47	9.287%	$196.1374	$196.14	$196.15	$196.10
Purchase #4	$182.38	9.513%	$199.7298	$199.73	$199.75	$199.70
Purchase #5	$143.99	10.224%	$158.7115	$158.71	$158.70	$158.70
Purchase #6	$74.25	12.706%	$83.6842	$83.68	$83.70	$83.70
Purchase #7	$43.96	5.540%	$46.3954	$46.40	$46.40	$46.40
7 purchase totals =	$1,007.49		$1,091.8598	$1,091.86	$1,091.90	$1,091.80