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	$123.90	13.455%	$140.5707	$140.57	$140.55	$140.60
Purchase #2	$155.29	7.686%	$167.2256	$167.23	$167.25	$167.20
Purchase #3	$6.74	7.775%	$7.264	$7.26	$7.25	$7.30
Purchase #4	$97.81	3.801%	$101.5278	$101.53	$101.55	$101.50
Purchase #5	$132.94	9.136%	$145.0854	$145.09	$145.10	$145.10
Purchase #6	$161.76	3.777%	$167.8697	$167.87	$167.85	$167.90
Purchase #7	$73.44	6.626%	$78.3061	$78.31	$78.30	$78.30
7 purchase totals =	$751.88		$807.8493	$807.86	$807.85	$807.90