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	$229.54	13.173%	$259.7773	$259.78	$259.80	$259.80
Purchase #2	$131.51	11.466%	$146.5889	$146.59	$146.60	$146.60
Purchase #3	$193.64	11.596%	$216.0945	$216.09	$216.10	$216.10
Purchase #4	$39.43	12.383%	$44.3126	$44.31	$44.30	$44.30
Purchase #5	$115.50	13.517%	$131.1121	$131.11	$131.10	$131.10
Purchase #6	$63.39	4.273%	$66.0987	$66.10	$66.10	$66.10
Purchase #7	$133.36	7.373%	$143.1926	$143.19	$143.20	$143.20
7 purchase totals =	$906.37		$1,007.1767	$1,007.17	$1,007.20	$1,007.20