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	$81.45	3.826%	$84.5663	$84.57	$84.55	$84.60
Purchase #2	$196.88	12.794%	$222.0688	$222.07	$222.05	$222.10
Purchase #3	$18.72	8.571%	$20.3245	$20.32	$20.30	$20.30
Purchase #4	$186.41	10.455%	$205.8992	$205.90	$205.90	$205.90
Purchase #5	$180.71	9.445%	$197.7781	$197.78	$197.80	$197.80
Purchase #6	$235.28	4.813%	$246.604	$246.60	$246.60	$246.60
Purchase #7	$227.72	7.527%	$244.8605	$244.86	$244.85	$244.90
7 purchase totals =	$1,127.17		$1,222.1014	$1,222.10	$1,222.05	$1,222.20