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	$150.38	13.418%	$170.558	$170.56	$170.55	$170.60
Purchase #2	$51.82	10.167%	$57.0885	$57.09	$57.10	$57.10
Purchase #3	$104.90	4.756%	$109.889	$109.89	$109.90	$109.90
Purchase #4	$125.92	5.331%	$132.6328	$132.63	$132.65	$132.60
Purchase #5	$171.55	10.175%	$189.0052	$189.01	$189.00	$189.00
Purchase #6	$119.39	8.113%	$129.0761	$129.08	$129.10	$129.10
Purchase #7	$68.52	5.313%	$72.1605	$72.16	$72.15	$72.20
7 purchase totals =	$792.48		$860.4101	$860.42	$860.45	$860.50