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	$238.78	12.475%	$268.5678	$268.57	$268.55	$268.60
Purchase #2	$177.69	5.111%	$186.7717	$186.77	$186.75	$186.80
Purchase #3	$198.49	12.311%	$222.9261	$222.93	$222.95	$222.90
Purchase #4	$52.60	3.485%	$54.4331	$54.43	$54.45	$54.40
Purchase #5	$125.79	13.280%	$142.4949	$142.49	$142.50	$142.50
Purchase #6	$125.31	9.262%	$136.9162	$136.92	$136.90	$136.90
Purchase #7	$54.84	12.736%	$61.8244	$61.82	$61.80	$61.80
7 purchase totals =	$973.50		$1,073.9342	$1,073.93	$1,073.90	$1,073.90