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	$61.96	13.804%	$70.513	$70.51	$70.50	$70.50
Purchase #2	$151.77	11.609%	$169.389	$169.39	$169.40	$169.40
Purchase #3	$132.63	8.306%	$143.6462	$143.65	$143.65	$143.60
Purchase #4	$17.52	7.144%	$18.7716	$18.77	$18.75	$18.80
Purchase #5	$75.60	3.353%	$78.1349	$78.13	$78.15	$78.10
Purchase #6	$175.67	4.326%	$183.2695	$183.27	$183.25	$183.30
Purchase #7	$119.34	5.703%	$126.146	$126.15	$126.15	$126.10
7 purchase totals =	$734.49		$789.8702	$789.87	$789.85	$789.80