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	$173.59	4.800%	$181.9223	$181.92	$181.90	$181.90
Purchase #2	$145.77	6.818%	$155.7086	$155.71	$155.70	$155.70
Purchase #3	$37.83	13.870%	$43.077	$43.08	$43.10	$43.10
Purchase #4	$39.94	3.768%	$41.4449	$41.44	$41.45	$41.40
Purchase #5	$250.36	11.619%	$279.4493	$279.45	$279.45	$279.40
Purchase #6	$167.38	13.283%	$189.6131	$189.61	$189.60	$189.60
Purchase #7	$112.25	5.254%	$118.1476	$118.15	$118.15	$118.10
7 purchase totals =	$927.12		$1,009.3628	$1,009.36	$1,009.35	$1,009.20