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	$231.83	13.320%	$262.7098	$262.71	$262.70	$262.70
Purchase #2	$52.83	12.451%	$59.4079	$59.41	$59.40	$59.40
Purchase #3	$236.86	11.796%	$264.8	$264.80	$264.80	$264.80
Purchase #4	$241.99	11.785%	$270.5085	$270.51	$270.50	$270.50
Purchase #5	$121.45	10.617%	$134.3443	$134.34	$134.35	$134.30
Purchase #6	$144.95	10.804%	$160.6104	$160.61	$160.60	$160.60
Purchase #7	$159.60	5.417%	$168.2455	$168.25	$168.25	$168.20
7 purchase totals =	$1,189.51		$1,320.6264	$1,320.63	$1,320.60	$1,320.50