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	$210.70	11.392%	$234.7029	$234.70	$234.70	$234.70
Purchase #2	$143.90	7.826%	$155.1616	$155.16	$155.15	$155.20
Purchase #3	$227.55	4.725%	$238.3017	$238.30	$238.30	$238.30
Purchase #4	$64.27	3.254%	$66.3613	$66.36	$66.35	$66.40
Purchase #5	$123.39	3.600%	$127.832	$127.83	$127.85	$127.80
Purchase #6	$58.69	5.348%	$61.8287	$61.83	$61.85	$61.80
Purchase #7	$94.92	10.342%	$104.7366	$104.74	$104.75	$104.70
7 purchase totals =	$923.42		$988.9248	$988.92	$988.95	$988.90