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	$73.40	9.252%	$80.191	$80.19	$80.20	$80.20
Purchase #2	$247.68	3.187%	$255.5736	$255.57	$255.55	$255.60
Purchase #3	$78.85	4.704%	$82.5591	$82.56	$82.55	$82.60
Purchase #4	$137.82	3.346%	$142.4315	$142.43	$142.45	$142.40
Purchase #5	$210.50	4.168%	$219.2736	$219.27	$219.25	$219.30
Purchase #6	$132.41	6.314%	$140.7704	$140.77	$140.75	$140.80
Purchase #7	$57.65	3.720%	$59.7946	$59.79	$59.80	$59.80
7 purchase totals =	$938.31		$980.5938	$980.58	$980.55	$980.70