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	$224.57	13.800%	$255.5607	$255.56	$255.55	$255.60
Purchase #2	$117.54	5.555%	$124.0693	$124.07	$124.05	$124.10
Purchase #3	$35.79	13.471%	$40.6113	$40.61	$40.60	$40.60
Purchase #4	$66.50	13.727%	$75.6285	$75.63	$75.65	$75.60
Purchase #5	$134.84	12.341%	$151.4806	$151.48	$151.50	$151.50
Purchase #6	$92.44	6.160%	$98.1343	$98.13	$98.15	$98.10
Purchase #7	$249.39	9.521%	$273.1344	$273.13	$273.15	$273.10
7 purchase totals =	$921.07		$1,018.6191	$1,018.61	$1,018.65	$1,018.60