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	$185.76	9.508%	$203.4221	$203.42	$203.40	$203.40
Purchase #2	$210.32	3.548%	$217.7822	$217.78	$217.80	$217.80
Purchase #3	$113.74	13.267%	$128.8299	$128.83	$128.85	$128.80
Purchase #4	$32.79	11.813%	$36.6635	$36.66	$36.65	$36.70
Purchase #5	$119.74	12.173%	$134.316	$134.32	$134.30	$134.30
Purchase #6	$244.43	6.122%	$259.394	$259.39	$259.40	$259.40
Purchase #7	$88.47	13.712%	$100.601	$100.60	$100.60	$100.60
7 purchase totals =	$995.25		$1,081.0087	$1,081.00	$1,081.00	$1,081.00