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	$34.50	12.836%	$38.9284	$38.93	$38.95	$38.90
Purchase #2	$62.32	13.292%	$70.6036	$70.60	$70.60	$70.60
Purchase #3	$137.87	13.248%	$156.135	$156.14	$156.15	$156.10
Purchase #4	$177.61	12.653%	$200.083	$200.08	$200.10	$200.10
Purchase #5	$103.28	10.261%	$113.8776	$113.88	$113.90	$113.90
Purchase #6	$213.58	3.172%	$220.3548	$220.35	$220.35	$220.40
Purchase #7	$160.56	6.858%	$171.5712	$171.57	$171.55	$171.60
7 purchase totals =	$889.72		$971.5536	$971.55	$971.60	$971.60