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	$37.70	11.196%	$41.9209	$41.92	$41.90	$41.90
Purchase #2	$138.70	10.711%	$153.5562	$153.56	$153.55	$153.60
Purchase #3	$40.82	10.443%	$45.0828	$45.08	$45.10	$45.10
Purchase #4	$60.95	7.770%	$65.6858	$65.69	$65.70	$65.70
Purchase #5	$217.42	5.415%	$229.1933	$229.19	$229.20	$229.20
Purchase #6	$117.73	9.229%	$128.5953	$128.60	$128.60	$128.60
Purchase #7	$117.35	8.594%	$127.4351	$127.44	$127.45	$127.40
7 purchase totals =	$730.67		$791.4694	$791.48	$791.50	$791.50