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	$129.74	5.322%	$136.6448	$136.64	$136.65	$136.60
Purchase #2	$228.57	5.859%	$241.9619	$241.96	$241.95	$242.00
Purchase #3	$134.73	3.507%	$139.455	$139.46	$139.45	$139.50
Purchase #4	$42.81	4.767%	$44.8508	$44.85	$44.85	$44.90
Purchase #5	$132.98	12.687%	$149.8512	$149.85	$149.85	$149.90
Purchase #6	$148.64	12.339%	$166.9807	$166.98	$167.00	$167.00
Purchase #7	$53.75	10.653%	$59.476	$59.48	$59.50	$59.50
7 purchase totals =	$871.22		$939.2204	$939.22	$939.25	$939.40