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	$104.26	8.628%	$113.2556	$113.26	$113.25	$113.30
Purchase #2	$19.43	6.686%	$20.7291	$20.73	$20.75	$20.70
Purchase #3	$40.86	4.708%	$42.7837	$42.78	$42.80	$42.80
Purchase #4	$38.76	10.496%	$42.8282	$42.83	$42.85	$42.80
Purchase #5	$204.61	8.390%	$221.7768	$221.78	$221.80	$221.80
Purchase #6	$151.73	5.326%	$159.8111	$159.81	$159.80	$159.80
Purchase #7	$30.70	3.395%	$31.7423	$31.74	$31.75	$31.70
7 purchase totals =	$590.35		$632.9268	$632.93	$633.00	$632.90