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	$234.31	11.655%	$261.6188	$261.62	$261.60	$261.60
Purchase #2	$39.85	6.473%	$42.4295	$42.43	$42.45	$42.40
Purchase #3	$27.82	12.821%	$31.3868	$31.39	$31.40	$31.40
Purchase #4	$220.94	7.664%	$237.8728	$237.87	$237.85	$237.90
Purchase #5	$204.89	11.718%	$228.899	$228.90	$228.90	$228.90
Purchase #6	$177.44	9.700%	$194.6517	$194.65	$194.65	$194.70
Purchase #7	$20.39	7.568%	$21.9331	$21.93	$21.95	$21.90
7 purchase totals =	$925.64		$1,018.7917	$1,018.79	$1,018.80	$1,018.80