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	$30.46	3.812%	$31.6211	$31.62	$31.60	$31.60
Purchase #2	$38.62	5.588%	$40.7781	$40.78	$40.80	$40.80
Purchase #3	$249.45	9.212%	$272.4293	$272.43	$272.45	$272.40
Purchase #4	$78.80	4.594%	$82.4201	$82.42	$82.40	$82.40
Purchase #5	$76.64	11.368%	$85.3524	$85.35	$85.35	$85.40
Purchase #6	$231.91	12.836%	$261.678	$261.68	$261.70	$261.70
Purchase #7	$6.96	13.638%	$7.9092	$7.91	$7.90	$7.90
7 purchase totals =	$712.84		$782.1882	$782.19	$782.20	$782.20