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	$132.38	8.125%	$143.1359	$143.14	$143.15	$143.10
Purchase #2	$56.40	9.112%	$61.5392	$61.54	$61.55	$61.50
Purchase #3	$139.78	11.633%	$156.0406	$156.04	$156.05	$156.00
Purchase #4	$95.85	8.620%	$104.1123	$104.11	$104.10	$104.10
Purchase #5	$11.90	5.167%	$12.5149	$12.51	$12.50	$12.50
Purchase #6	$149.82	12.582%	$168.6704	$168.67	$168.65	$168.70
Purchase #7	$175.55	4.380%	$183.2391	$183.24	$183.25	$183.20
7 purchase totals =	$761.68		$829.2524	$829.25	$829.25	$829.10