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	$162.57	12.859%	$183.4749	$183.47	$183.45	$183.50
Purchase #2	$160.52	6.283%	$170.6055	$170.61	$170.60	$170.60
Purchase #3	$38.69	9.500%	$42.3656	$42.37	$42.35	$42.40
Purchase #4	$66.72	9.173%	$72.8402	$72.84	$72.85	$72.80
Purchase #5	$117.31	5.772%	$124.0811	$124.08	$124.10	$124.10
Purchase #6	$193.77	11.231%	$215.5323	$215.53	$215.55	$215.50
Purchase #7	$152.88	9.553%	$167.4846	$167.48	$167.50	$167.50
7 purchase totals =	$892.46		$976.3842	$976.38	$976.40	$976.40