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	$48.93	11.813%	$54.7101	$54.71	$54.70	$54.70
Purchase #2	$246.90	10.324%	$272.39	$272.39	$272.40	$272.40
Purchase #3	$158.82	8.189%	$171.8258	$171.83	$171.85	$171.80
Purchase #4	$178.72	4.203%	$186.2316	$186.23	$186.25	$186.20
Purchase #5	$90.85	4.472%	$94.9128	$94.91	$94.90	$94.90
Purchase #6	$185.71	4.338%	$193.7661	$193.77	$193.75	$193.80
Purchase #7	$104.69	7.500%	$112.5418	$112.54	$112.55	$112.50
7 purchase totals =	$1,014.62		$1,086.3782	$1,086.38	$1,086.40	$1,086.30