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	$121.70	3.839%	$126.3721	$126.37	$126.35	$126.40
Purchase #2	$111.80	11.460%	$124.6123	$124.61	$124.60	$124.60
Purchase #3	$132.60	5.338%	$139.6782	$139.68	$139.70	$139.70
Purchase #4	$237.55	4.329%	$247.8335	$247.83	$247.85	$247.80
Purchase #5	$132.72	12.213%	$148.9291	$148.93	$148.95	$148.90
Purchase #6	$119.77	6.285%	$127.2975	$127.30	$127.30	$127.30
Purchase #7	$59.74	9.779%	$65.582	$65.58	$65.60	$65.60
7 purchase totals =	$915.88		$980.3047	$980.30	$980.35	$980.30