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	$40.96	11.467%	$45.6569	$45.66	$45.65	$45.70
Purchase #2	$38.25	4.354%	$39.9154	$39.92	$39.90	$39.90
Purchase #3	$178.41	6.783%	$190.5116	$190.51	$190.50	$190.50
Purchase #4	$119.51	5.238%	$125.7699	$125.77	$125.75	$125.80
Purchase #5	$198.37	4.548%	$207.3919	$207.39	$207.40	$207.40
Purchase #6	$113.66	10.509%	$125.6045	$125.60	$125.60	$125.60
Purchase #7	$89.35	11.634%	$99.745	$99.75	$99.75	$99.70
7 purchase totals =	$778.51		$834.5952	$834.60	$834.55	$834.60