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	$220.52	4.123%	$229.612	$229.61	$229.60	$229.60
Purchase #2	$137.25	12.195%	$153.9876	$153.99	$154.00	$154.00
Purchase #3	$131.68	6.626%	$140.4051	$140.41	$140.40	$140.40
Purchase #4	$84.31	10.627%	$93.2696	$93.27	$93.25	$93.30
Purchase #5	$82.47	4.839%	$86.4607	$86.46	$86.45	$86.50
Purchase #6	$30.52	10.517%	$33.7298	$33.73	$33.75	$33.70
Purchase #7	$156.77	3.857%	$162.8166	$162.82	$162.80	$162.80
7 purchase totals =	$843.52		$900.2814	$900.29	$900.25	$900.30