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	$16.91	10.213%	$18.637	$18.64	$18.65	$18.60
Purchase #2	$245.32	6.351%	$260.9003	$260.90	$260.90	$260.90
Purchase #3	$217.92	11.750%	$243.5256	$243.53	$243.55	$243.50
Purchase #4	$118.86	10.494%	$131.3332	$131.33	$131.35	$131.30
Purchase #5	$173.52	6.168%	$184.2227	$184.22	$184.20	$184.20
Purchase #6	$170.62	12.746%	$192.3672	$192.37	$192.35	$192.40
Purchase #7	$101.51	10.297%	$111.9625	$111.96	$111.95	$112.00
7 purchase totals =	$1,044.66		$1,142.9485	$1,142.95	$1,142.95	$1,142.90