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	$138.78	3.517%	$143.6609	$143.66	$143.65	$143.70
Purchase #2	$227.56	6.517%	$242.3901	$242.39	$242.40	$242.40
Purchase #3	$98.96	4.462%	$103.3756	$103.38	$103.40	$103.40
Purchase #4	$59.60	9.186%	$65.0749	$65.07	$65.05	$65.10
Purchase #5	$122.81	9.602%	$134.6022	$134.60	$134.60	$134.60
Purchase #6	$141.64	9.124%	$154.5632	$154.56	$154.55	$154.60
Purchase #7	$177.48	10.829%	$196.6993	$196.70	$196.70	$196.70
7 purchase totals =	$966.83		$1,040.3662	$1,040.36	$1,040.35	$1,040.50