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	$118.47	8.665%	$128.7354	$128.74	$128.75	$128.70
Purchase #2	$207.25	13.827%	$235.9065	$235.91	$235.90	$235.90
Purchase #3	$94.61	6.231%	$100.5051	$100.51	$100.50	$100.50
Purchase #4	$47.88	7.712%	$51.5725	$51.57	$51.55	$51.60
Purchase #5	$127.95	13.537%	$145.2706	$145.27	$145.25	$145.30
Purchase #6	$167.25	11.533%	$186.5389	$186.54	$186.55	$186.50
Purchase #7	$229.27	5.517%	$241.9188	$241.92	$241.90	$241.90
7 purchase totals =	$992.68		$1,090.4478	$1,090.46	$1,090.40	$1,090.40