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	$74.84	13.859%	$85.2121	$85.21	$85.20	$85.20
Purchase #2	$210.99	6.854%	$225.4513	$225.45	$225.45	$225.50
Purchase #3	$208.50	7.357%	$223.8393	$223.84	$223.85	$223.80
Purchase #4	$100.72	5.499%	$106.2586	$106.26	$106.25	$106.30
Purchase #5	$39.25	8.187%	$42.4634	$42.46	$42.45	$42.50
Purchase #6	$37.28	13.788%	$42.4202	$42.42	$42.40	$42.40
Purchase #7	$48.30	9.754%	$53.0112	$53.01	$53.00	$53.00
7 purchase totals =	$719.88		$778.6561	$778.65	$778.60	$778.70