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	$81.65	9.120%	$89.0965	$89.10	$89.10	$89.10
Purchase #2	$52.45	8.470%	$56.8925	$56.89	$56.90	$56.90
Purchase #3	$78.71	3.552%	$81.5058	$81.51	$81.50	$81.50
Purchase #4	$58.71	12.344%	$65.9572	$65.96	$65.95	$66.00
Purchase #5	$115.64	6.727%	$123.4191	$123.42	$123.40	$123.40
Purchase #6	$100.37	7.787%	$108.1858	$108.19	$108.20	$108.20
Purchase #7	$58.53	11.694%	$65.3745	$65.37	$65.35	$65.40
7 purchase totals =	$546.06		$590.4314	$590.44	$590.40	$590.50