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	$58.31	13.180%	$65.9953	$66.00	$66.00	$66.00
Purchase #2	$126.30	13.536%	$143.396	$143.40	$143.40	$143.40
Purchase #3	$94.46	7.317%	$101.3716	$101.37	$101.35	$101.40
Purchase #4	$46.33	13.186%	$52.4391	$52.44	$52.45	$52.40
Purchase #5	$105.27	5.860%	$111.4388	$111.44	$111.45	$111.40
Purchase #6	$31.44	12.177%	$35.2684	$35.27	$35.25	$35.30
Purchase #7	$232.75	13.352%	$263.8268	$263.83	$263.85	$263.80
7 purchase totals =	$694.86		$773.7360	$773.75	$773.75	$773.70