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	$24.37	13.712%	$27.7116	$27.71	$27.70	$27.70
Purchase #2	$78.25	10.818%	$86.7151	$86.72	$86.70	$86.70
Purchase #3	$187.71	6.262%	$199.4644	$199.46	$199.45	$199.50
Purchase #4	$172.81	8.438%	$187.3917	$187.39	$187.40	$187.40
Purchase #5	$198.89	12.380%	$223.5126	$223.51	$223.50	$223.50
Purchase #6	$241.76	7.536%	$259.979	$259.98	$260.00	$260.00
Purchase #7	$44.83	10.143%	$49.3771	$49.38	$49.40	$49.40
7 purchase totals =	$948.62		$1,034.1515	$1,034.15	$1,034.15	$1,034.20