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	$40.29	7.304%	$43.2328	$43.23	$43.25	$43.20
Purchase #2	$198.92	11.833%	$222.4582	$222.46	$222.45	$222.50
Purchase #3	$118.51	13.150%	$134.0941	$134.09	$134.10	$134.10
Purchase #4	$145.29	3.697%	$150.6614	$150.66	$150.65	$150.70
Purchase #5	$68.53	3.811%	$71.1417	$71.14	$71.15	$71.10
Purchase #6	$229.60	7.389%	$246.5651	$246.57	$246.55	$246.60
Purchase #7	$22.54	7.145%	$24.1505	$24.15	$24.15	$24.20
7 purchase totals =	$823.68		$892.3038	$892.30	$892.30	$892.40