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	$149.68	12.603%	$168.5442	$168.54	$168.55	$168.50
Purchase #2	$220.60	4.718%	$231.0079	$231.01	$231.00	$231.00
Purchase #3	$218.82	12.120%	$245.341	$245.34	$245.35	$245.30
Purchase #4	$249.75	11.434%	$278.3064	$278.31	$278.30	$278.30
Purchase #5	$178.72	9.868%	$196.3561	$196.36	$196.35	$196.40
Purchase #6	$70.42	11.708%	$78.6648	$78.66	$78.65	$78.70
Purchase #7	$133.40	3.741%	$138.3905	$138.39	$138.40	$138.40
7 purchase totals =	$1,221.39		$1,336.6109	$1,336.61	$1,336.60	$1,336.60