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	$25.90	5.363%	$27.289	$27.29	$27.30	$27.30
Purchase #2	$150.99	3.719%	$156.6053	$156.61	$156.60	$156.60
Purchase #3	$185.67	10.495%	$205.1561	$205.16	$205.15	$205.20
Purchase #4	$115.52	10.376%	$127.5064	$127.51	$127.50	$127.50
Purchase #5	$199.56	5.293%	$210.1227	$210.12	$210.10	$210.10
Purchase #6	$90.31	12.341%	$101.4552	$101.46	$101.45	$101.50
Purchase #7	$207.56	11.298%	$231.0101	$231.01	$231.00	$231.00
7 purchase totals =	$975.51		$1,059.1448	$1,059.16	$1,059.10	$1,059.20