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	9.590%	$166.522	$166.52	$166.50	$166.50
Purchase #2	$198.82	3.720%	$206.2161	$206.22	$206.20	$206.20
Purchase #3	$13.69	13.467%	$15.5336	$15.53	$15.55	$15.50
Purchase #4	$7.90	4.361%	$8.2445	$8.24	$8.25	$8.20
Purchase #5	$83.70	8.449%	$90.7718	$90.77	$90.75	$90.80
Purchase #6	$123.65	10.687%	$136.8645	$136.86	$136.85	$136.90
Purchase #7	$248.34	4.443%	$259.3737	$259.37	$259.35	$259.40
7 purchase totals =	$828.05		$883.5262	$883.51	$883.45	$883.50