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	$120.54	5.846%	$127.5868	$127.59	$127.60	$127.60
Purchase #2	$181.54	7.500%	$195.1555	$195.16	$195.15	$195.20
Purchase #3	$9.76	11.585%	$10.8907	$10.89	$10.90	$10.90
Purchase #4	$34.73	11.115%	$38.5902	$38.59	$38.60	$38.60
Purchase #5	$186.77	11.574%	$208.3868	$208.39	$208.40	$208.40
Purchase #6	$21.74	8.778%	$23.6483	$23.65	$23.65	$23.60
Purchase #7	$61.66	6.769%	$65.8338	$65.83	$65.85	$65.80
7 purchase totals =	$616.74		$670.0921	$670.10	$670.15	$670.10