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	$174.50	6.357%	$185.593	$185.59	$185.60	$185.60
Purchase #2	$147.91	7.581%	$159.1231	$159.12	$159.10	$159.10
Purchase #3	$121.64	6.461%	$129.4992	$129.50	$129.50	$129.50
Purchase #4	$206.59	10.649%	$228.5898	$228.59	$228.60	$228.60
Purchase #5	$100.62	4.861%	$105.5111	$105.51	$105.50	$105.50
Purchase #6	$50.88	6.520%	$54.1974	$54.20	$54.20	$54.20
Purchase #7	$18.49	4.581%	$19.337	$19.34	$19.35	$19.30
7 purchase totals =	$820.63		$881.8506	$881.85	$881.85	$881.80