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	$237.47	9.389%	$259.7661	$259.77	$259.75	$259.80
Purchase #2	$142.31	5.851%	$150.6366	$150.64	$150.65	$150.60
Purchase #3	$250.43	6.549%	$266.8307	$266.83	$266.85	$266.80
Purchase #4	$133.69	3.545%	$138.4293	$138.43	$138.45	$138.40
Purchase #5	$152.27	9.235%	$166.3321	$166.33	$166.35	$166.30
Purchase #6	$54.46	12.466%	$61.249	$61.25	$61.25	$61.20
Purchase #7	$13.96	5.444%	$14.72	$14.72	$14.70	$14.70
7 purchase totals =	$984.59		$1,057.9638	$1,057.97	$1,058.00	$1,057.80