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	$51.82	4.214%	$54.0037	$54.00	$54.00	$54.00
Purchase #2	$176.36	7.658%	$189.8656	$189.87	$189.85	$189.90
Purchase #3	$160.46	8.521%	$174.1328	$174.13	$174.15	$174.10
Purchase #4	$27.32	7.641%	$29.4075	$29.41	$29.40	$29.40
Purchase #5	$91.43	9.444%	$100.0646	$100.06	$100.05	$100.10
Purchase #6	$233.60	11.655%	$260.8261	$260.83	$260.85	$260.80
Purchase #7	$178.80	9.755%	$196.2419	$196.24	$196.25	$196.20
7 purchase totals =	$919.79		$1,004.5422	$1,004.54	$1,004.55	$1,004.50