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	$57.90	6.153%	$61.4626	$61.46	$61.45	$61.50
Purchase #2	$132.29	5.534%	$139.6109	$139.61	$139.60	$139.60
Purchase #3	$107.52	4.251%	$112.0907	$112.09	$112.10	$112.10
Purchase #4	$143.75	8.221%	$155.5677	$155.57	$155.55	$155.60
Purchase #5	$164.35	7.636%	$176.8998	$176.90	$176.90	$176.90
Purchase #6	$72.93	10.825%	$80.8247	$80.82	$80.80	$80.80
Purchase #7	$173.37	13.288%	$196.4074	$196.41	$196.40	$196.40
7 purchase totals =	$852.11		$922.8638	$922.86	$922.80	$922.90