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	$125.46	12.600%	$141.268	$141.27	$141.25	$141.30
Purchase #2	$194.51	10.443%	$214.8227	$214.82	$214.80	$214.80
Purchase #3	$85.86	5.262%	$90.378	$90.38	$90.40	$90.40
Purchase #4	$67.59	4.444%	$70.5937	$70.59	$70.60	$70.60
Purchase #5	$28.72	10.611%	$31.7675	$31.77	$31.75	$31.80
Purchase #6	$140.85	4.786%	$147.5911	$147.59	$147.60	$147.60
Purchase #7	$176.34	9.526%	$193.1381	$193.14	$193.15	$193.10
7 purchase totals =	$819.33		$889.5591	$889.56	$889.55	$889.60