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	$150.39	5.596%	$158.8058	$158.81	$158.80	$158.80
Purchase #2	$137.70	8.126%	$148.8895	$148.89	$148.90	$148.90
Purchase #3	$161.75	9.446%	$177.0289	$177.03	$177.05	$177.00
Purchase #4	$68.92	13.649%	$78.3269	$78.33	$78.35	$78.30
Purchase #5	$102.37	7.773%	$110.3272	$110.33	$110.35	$110.30
Purchase #6	$70.72	13.776%	$80.4624	$80.46	$80.45	$80.50
Purchase #7	$195.64	10.112%	$215.4231	$215.42	$215.40	$215.40
7 purchase totals =	$887.49		$969.2638	$969.27	$969.30	$969.20