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	$244.89	13.454%	$277.8375	$277.84	$277.85	$277.80
Purchase #2	$176.75	5.525%	$186.5154	$186.52	$186.50	$186.50
Purchase #3	$70.44	13.260%	$79.7803	$79.78	$79.80	$79.80
Purchase #4	$116.95	9.121%	$127.617	$127.62	$127.60	$127.60
Purchase #5	$164.97	5.254%	$173.6375	$173.64	$173.65	$173.60
Purchase #6	$36.86	13.409%	$41.8026	$41.80	$41.80	$41.80
Purchase #7	$124.50	5.617%	$131.4932	$131.49	$131.50	$131.50
7 purchase totals =	$935.36		$1,018.6835	$1,018.69	$1,018.70	$1,018.60