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	$155.45	3.308%	$160.5923	$160.59	$160.60	$160.60
Purchase #2	$226.95	8.481%	$246.1976	$246.20	$246.20	$246.20
Purchase #3	$151.78	12.615%	$170.927	$170.93	$170.95	$170.90
Purchase #4	$81.85	10.454%	$90.4066	$90.41	$90.40	$90.40
Purchase #5	$242.94	12.595%	$273.5383	$273.54	$273.55	$273.50
Purchase #6	$7.57	3.653%	$7.8465	$7.85	$7.85	$7.80
Purchase #7	$219.50	5.406%	$231.3662	$231.37	$231.35	$231.40
7 purchase totals =	$1,086.04		$1,180.8745	$1,180.89	$1,180.90	$1,180.80