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	$113.95	5.694%	$120.4383	$120.44	$120.45	$120.40
Purchase #2	$35.53	5.672%	$37.5453	$37.55	$37.55	$37.50
Purchase #3	$5.57	11.715%	$6.2225	$6.22	$6.20	$6.20
Purchase #4	$167.95	10.661%	$185.8551	$185.86	$185.85	$185.90
Purchase #5	$50.42	8.138%	$54.5232	$54.52	$54.50	$54.50
Purchase #6	$80.88	9.240%	$88.3533	$88.35	$88.35	$88.40
Purchase #7	$124.63	9.665%	$136.6755	$136.68	$136.70	$136.70
7 purchase totals =	$578.93		$629.6132	$629.62	$629.60	$629.60