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	$19.52	11.483%	$21.7615	$21.76	$21.75	$21.80
Purchase #2	$181.26	8.269%	$196.2484	$196.25	$196.25	$196.20
Purchase #3	$126.89	11.550%	$141.5458	$141.55	$141.55	$141.50
Purchase #4	$77.41	12.726%	$87.2612	$87.26	$87.25	$87.30
Purchase #5	$176.91	10.165%	$194.8929	$194.89	$194.90	$194.90
Purchase #6	$213.40	13.148%	$241.4578	$241.46	$241.45	$241.50
Purchase #7	$178.63	7.543%	$192.1041	$192.10	$192.10	$192.10
7 purchase totals =	$974.02		$1,075.2717	$1,075.27	$1,075.25	$1,075.30