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	$122.37	3.453%	$126.5954	$126.60	$126.60	$126.60
Purchase #2	$125.69	6.311%	$133.6223	$133.62	$133.60	$133.60
Purchase #3	$127.85	3.141%	$131.8658	$131.87	$131.85	$131.90
Purchase #4	$59.46	3.513%	$61.5488	$61.55	$61.55	$61.50
Purchase #5	$118.91	7.866%	$128.2635	$128.26	$128.25	$128.30
Purchase #6	$19.35	5.625%	$20.4384	$20.44	$20.45	$20.40
Purchase #7	$36.47	6.476%	$38.8318	$38.83	$38.85	$38.80
7 purchase totals =	$610.10		$641.1660	$641.17	$641.15	$641.10