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	$248.79	10.284%	$274.3756	$274.38	$274.40	$274.40
Purchase #2	$23.34	5.248%	$24.5649	$24.56	$24.55	$24.60
Purchase #3	$75.68	3.595%	$78.4007	$78.40	$78.40	$78.40
Purchase #4	$104.55	11.211%	$116.2711	$116.27	$116.25	$116.30
Purchase #5	$56.70	13.693%	$64.4639	$64.46	$64.45	$64.50
Purchase #6	$159.40	13.735%	$181.2936	$181.29	$181.30	$181.30
Purchase #7	$205.41	11.742%	$229.5292	$229.53	$229.55	$229.50
7 purchase totals =	$873.87		$968.8990	$968.89	$968.90	$969.00