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	$152.48	9.319%	$166.6896	$166.69	$166.70	$166.70
Purchase #2	$183.73	4.208%	$191.4614	$191.46	$191.45	$191.50
Purchase #3	$148.65	13.687%	$168.9957	$169.00	$169.00	$169.00
Purchase #4	$33.93	13.543%	$38.5251	$38.53	$38.55	$38.50
Purchase #5	$34.48	5.735%	$36.4574	$36.46	$36.45	$36.50
Purchase #6	$142.87	11.859%	$159.813	$159.81	$159.80	$159.80
Purchase #7	$24.26	13.720%	$27.5885	$27.59	$27.60	$27.60
7 purchase totals =	$720.40		$789.5307	$789.54	$789.55	$789.60