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	$30.67	10.296%	$33.8278	$33.83	$33.85	$33.80
Purchase #2	$114.66	11.535%	$127.886	$127.89	$127.90	$127.90
Purchase #3	$211.43	5.120%	$222.2552	$222.26	$222.25	$222.30
Purchase #4	$68.69	6.845%	$73.3918	$73.39	$73.40	$73.40
Purchase #5	$25.37	8.755%	$27.5911	$27.59	$27.60	$27.60
Purchase #6	$31.42	11.707%	$35.0983	$35.10	$35.10	$35.10
Purchase #7	$142.90	7.196%	$153.1831	$153.18	$153.20	$153.20
7 purchase totals =	$625.14		$673.2333	$673.24	$673.30	$673.30