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	$221.61	13.128%	$250.703	$250.70	$250.70	$250.70
Purchase #2	$36.63	10.616%	$40.5186	$40.52	$40.50	$40.50
Purchase #3	$49.42	6.381%	$52.5735	$52.57	$52.55	$52.60
Purchase #4	$100.35	9.382%	$109.7648	$109.76	$109.75	$109.80
Purchase #5	$180.66	6.149%	$191.7688	$191.77	$191.75	$191.80
Purchase #6	$158.42	9.264%	$173.096	$173.10	$173.10	$173.10
Purchase #7	$73.90	9.111%	$80.633	$80.63	$80.65	$80.60
7 purchase totals =	$820.99		$899.0577	$899.05	$899.00	$899.10