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	$151.95	8.474%	$164.8262	$164.83	$164.85	$164.80
Purchase #2	$137.88	9.377%	$150.809	$150.81	$150.80	$150.80
Purchase #3	$161.60	5.252%	$170.0872	$170.09	$170.10	$170.10
Purchase #4	$186.63	4.170%	$194.4125	$194.41	$194.40	$194.40
Purchase #5	$103.53	8.774%	$112.6137	$112.61	$112.60	$112.60
Purchase #6	$211.86	11.638%	$236.5163	$236.52	$236.50	$236.50
Purchase #7	$225.59	13.158%	$255.2731	$255.27	$255.25	$255.30
7 purchase totals =	$1,179.04		$1,284.5380	$1,284.54	$1,284.50	$1,284.50