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	$111.76	7.391%	$120.0202	$120.02	$120.00	$120.00
Purchase #2	$177.31	10.582%	$196.0729	$196.07	$196.05	$196.10
Purchase #3	$65.31	3.232%	$67.4208	$67.42	$67.40	$67.40
Purchase #4	$160.86	9.496%	$176.1353	$176.14	$176.15	$176.10
Purchase #5	$128.92	9.457%	$141.112	$141.11	$141.10	$141.10
Purchase #6	$107.72	9.757%	$118.2302	$118.23	$118.25	$118.20
Purchase #7	$113.99	11.429%	$127.0179	$127.02	$127.00	$127.00
7 purchase totals =	$865.87		$946.0093	$946.01	$945.95	$945.90