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	$42.36	6.697%	$45.1968	$45.20	$45.20	$45.20
Purchase #2	$107.59	8.812%	$117.0708	$117.07	$117.05	$117.10
Purchase #3	$171.91	4.619%	$179.8505	$179.85	$179.85	$179.90
Purchase #4	$119.65	13.790%	$136.1497	$136.15	$136.15	$136.10
Purchase #5	$25.90	5.442%	$27.3095	$27.31	$27.30	$27.30
Purchase #6	$62.89	3.450%	$65.0597	$65.06	$65.05	$65.10
Purchase #7	$102.87	8.209%	$111.3146	$111.31	$111.30	$111.30
7 purchase totals =	$633.17		$681.9516	$681.95	$681.90	$682.00