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	$124.80	11.810%	$139.5389	$139.54	$139.55	$139.50
Purchase #2	$189.30	10.807%	$209.7577	$209.76	$209.75	$209.80
Purchase #3	$20.33	4.539%	$21.2528	$21.25	$21.25	$21.30
Purchase #4	$155.76	13.242%	$176.3857	$176.39	$176.40	$176.40
Purchase #5	$139.40	8.315%	$150.9911	$150.99	$151.00	$151.00
Purchase #6	$78.88	3.455%	$81.6053	$81.61	$81.60	$81.60
Purchase #7	$47.27	12.153%	$53.0147	$53.01	$53.00	$53.00
7 purchase totals =	$755.74		$832.5462	$832.55	$832.55	$832.60