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	$242.58	13.418%	$275.1294	$275.13	$275.15	$275.10
Purchase #2	$143.39	11.380%	$159.7078	$159.71	$159.70	$159.70
Purchase #3	$233.83	9.442%	$255.9082	$255.91	$255.90	$255.90
Purchase #4	$29.70	12.664%	$33.4612	$33.46	$33.45	$33.50
Purchase #5	$62.65	11.535%	$69.8767	$69.88	$69.90	$69.90
Purchase #6	$20.82	8.482%	$22.586	$22.59	$22.60	$22.60
Purchase #7	$175.99	9.353%	$192.4503	$192.45	$192.45	$192.50
7 purchase totals =	$908.96		$1,009.1196	$1,009.13	$1,009.15	$1,009.20