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	$72.77	11.302%	$80.9945	$80.99	$81.00	$81.00
Purchase #2	$91.25	13.354%	$103.4355	$103.44	$103.45	$103.40
Purchase #3	$244.66	5.838%	$258.9433	$258.94	$258.95	$258.90
Purchase #4	$56.98	10.246%	$62.8182	$62.82	$62.80	$62.80
Purchase #5	$53.70	10.665%	$59.4271	$59.43	$59.45	$59.40
Purchase #6	$159.51	4.349%	$166.4471	$166.45	$166.45	$166.40
Purchase #7	$125.85	9.389%	$137.6661	$137.67	$137.65	$137.70
7 purchase totals =	$804.72		$869.7318	$869.74	$869.75	$869.60