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	$200.28	6.794%	$213.887	$213.89	$213.90	$213.90
Purchase #2	$101.99	9.192%	$111.3649	$111.36	$111.35	$111.40
Purchase #3	$103.80	5.542%	$109.5526	$109.55	$109.55	$109.60
Purchase #4	$186.37	11.848%	$208.4511	$208.45	$208.45	$208.50
Purchase #5	$109.59	12.704%	$123.5123	$123.51	$123.50	$123.50
Purchase #6	$30.42	4.212%	$31.7013	$31.70	$31.70	$31.70
Purchase #7	$84.74	6.362%	$90.1312	$90.13	$90.15	$90.10
7 purchase totals =	$817.19		$888.6004	$888.59	$888.60	$888.70