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	$20.84	9.866%	$22.8961	$22.90	$22.90	$22.90
Purchase #2	$172.27	10.357%	$190.112	$190.11	$190.10	$190.10
Purchase #3	$102.63	13.171%	$116.1474	$116.15	$116.15	$116.10
Purchase #4	$127.54	12.474%	$143.4493	$143.45	$143.45	$143.40
Purchase #5	$32.33	4.780%	$33.8754	$33.88	$33.90	$33.90
Purchase #6	$66.36	4.721%	$69.4929	$69.49	$69.50	$69.50
Purchase #7	$176.83	12.304%	$198.5872	$198.59	$198.60	$198.60
7 purchase totals =	$698.80		$774.5603	$774.57	$774.60	$774.50