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	$22.45	9.146%	$24.5033	$24.50	$24.50	$24.50
Purchase #2	$159.72	5.289%	$168.1676	$168.17	$168.15	$168.20
Purchase #3	$173.74	13.730%	$197.5945	$197.59	$197.60	$197.60
Purchase #4	$37.42	8.826%	$40.7227	$40.72	$40.70	$40.70
Purchase #5	$72.33	8.486%	$78.4679	$78.47	$78.45	$78.50
Purchase #6	$235.40	4.362%	$245.6681	$245.67	$245.65	$245.70
Purchase #7	$177.39	5.184%	$186.5859	$186.59	$186.60	$186.60
7 purchase totals =	$878.45		$941.7100	$941.71	$941.65	$941.80