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	$236.34	9.700%	$259.265	$259.27	$259.25	$259.30
Purchase #2	$118.71	7.375%	$127.4649	$127.46	$127.45	$127.50
Purchase #3	$194.57	10.466%	$214.9337	$214.93	$214.95	$214.90
Purchase #4	$171.59	12.745%	$193.4591	$193.46	$193.45	$193.50
Purchase #5	$69.51	5.144%	$73.0856	$73.09	$73.10	$73.10
Purchase #6	$145.84	12.567%	$164.1677	$164.17	$164.15	$164.20
Purchase #7	$45.93	6.275%	$48.8121	$48.81	$48.80	$48.80
7 purchase totals =	$982.49		$1,081.1881	$1,081.19	$1,081.15	$1,081.30