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	$96.54	6.252%	$102.5757	$102.58	$102.60	$102.60
Purchase #2	$142.47	9.433%	$155.9092	$155.91	$155.90	$155.90
Purchase #3	$218.37	4.296%	$227.7512	$227.75	$227.75	$227.80
Purchase #4	$185.26	8.745%	$201.461	$201.46	$201.45	$201.50
Purchase #5	$103.68	7.757%	$111.7225	$111.72	$111.70	$111.70
Purchase #6	$146.28	6.302%	$155.4986	$155.50	$155.50	$155.50
Purchase #7	$55.56	9.558%	$60.8704	$60.87	$60.85	$60.90
7 purchase totals =	$948.16		$1,015.7886	$1,015.79	$1,015.75	$1,015.90