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	$37.74	8.315%	$40.8781	$40.88	$40.90	$40.90
Purchase #2	$123.79	6.592%	$131.9502	$131.95	$131.95	$132.00
Purchase #3	$119.72	10.717%	$132.5504	$132.55	$132.55	$132.60
Purchase #4	$107.56	9.645%	$117.9342	$117.93	$117.95	$117.90
Purchase #5	$151.78	10.422%	$167.5985	$167.60	$167.60	$167.60
Purchase #6	$98.80	9.175%	$107.8649	$107.86	$107.85	$107.90
Purchase #7	$56.44	5.649%	$59.6283	$59.63	$59.65	$59.60
7 purchase totals =	$695.83		$758.4046	$758.40	$758.45	$758.50