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	$43.43	4.806%	$45.5172	$45.52	$45.50	$45.50
Purchase #2	$43.77	13.841%	$49.8282	$49.83	$49.85	$49.80
Purchase #3	$42.58	13.686%	$48.4075	$48.41	$48.40	$48.40
Purchase #4	$98.81	3.595%	$102.3622	$102.36	$102.35	$102.40
Purchase #5	$164.92	9.611%	$180.7705	$180.77	$180.75	$180.80
Purchase #6	$86.84	12.114%	$97.3598	$97.36	$97.35	$97.40
Purchase #7	$117.89	8.260%	$127.6277	$127.63	$127.65	$127.60
7 purchase totals =	$598.24		$651.8731	$651.88	$651.85	$651.90