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	$172.81	6.871%	$184.6838	$184.68	$184.70	$184.70
Purchase #2	$218.91	8.755%	$238.0756	$238.08	$238.10	$238.10
Purchase #3	$114.47	11.482%	$127.6134	$127.61	$127.60	$127.60
Purchase #4	$59.82	7.631%	$64.3849	$64.38	$64.40	$64.40
Purchase #5	$190.75	3.226%	$196.9036	$196.90	$196.90	$196.90
Purchase #6	$40.25	9.243%	$43.9703	$43.97	$43.95	$44.00
Purchase #7	$64.54	3.120%	$66.5536	$66.55	$66.55	$66.60
7 purchase totals =	$861.55		$922.1852	$922.17	$922.20	$922.30