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	$122.45	12.143%	$137.3191	$137.32	$137.30	$137.30
Purchase #2	$76.73	10.374%	$84.69	$84.69	$84.70	$84.70
Purchase #3	$120.38	13.651%	$136.8131	$136.81	$136.80	$136.80
Purchase #4	$131.29	11.152%	$145.9315	$145.93	$145.95	$145.90
Purchase #5	$246.66	6.261%	$262.1034	$262.10	$262.10	$262.10
Purchase #6	$158.36	6.240%	$168.2417	$168.24	$168.25	$168.20
Purchase #7	$40.90	6.305%	$43.4787	$43.48	$43.50	$43.50
7 purchase totals =	$896.77		$978.5775	$978.57	$978.60	$978.50