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	$76.95	5.781%	$81.3985	$81.40	$81.40	$81.40
Purchase #2	$158.27	10.218%	$174.442	$174.44	$174.45	$174.40
Purchase #3	$199.58	3.584%	$206.7329	$206.73	$206.75	$206.70
Purchase #4	$77.70	13.760%	$88.3915	$88.39	$88.40	$88.40
Purchase #5	$41.45	3.162%	$42.7606	$42.76	$42.75	$42.80
Purchase #6	$174.28	6.398%	$185.4304	$185.43	$185.45	$185.40
Purchase #7	$108.67	13.558%	$123.4035	$123.40	$123.40	$123.40
7 purchase totals =	$836.90		$902.5594	$902.55	$902.60	$902.50