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	$81.68	9.761%	$89.6528	$89.65	$89.65	$89.70
Purchase #2	$107.47	4.730%	$112.5533	$112.55	$112.55	$112.60
Purchase #3	$44.34	12.467%	$49.8679	$49.87	$49.85	$49.90
Purchase #4	$81.57	9.167%	$89.0475	$89.05	$89.05	$89.00
Purchase #5	$209.56	11.369%	$233.3849	$233.38	$233.40	$233.40
Purchase #6	$144.86	10.295%	$159.7733	$159.77	$159.75	$159.80
Purchase #7	$136.38	13.384%	$154.6331	$154.63	$154.65	$154.60
7 purchase totals =	$805.86		$888.9128	$888.90	$888.90	$889.00