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	$48.29	13.792%	$54.9502	$54.95	$54.95	$55.00
Purchase #2	$181.99	8.702%	$197.8268	$197.83	$197.85	$197.80
Purchase #3	$246.50	8.861%	$268.3424	$268.34	$268.35	$268.30
Purchase #4	$51.48	6.751%	$54.9554	$54.96	$54.95	$55.00
Purchase #5	$51.93	4.255%	$54.1396	$54.14	$54.15	$54.10
Purchase #6	$86.68	3.263%	$89.5084	$89.51	$89.50	$89.50
Purchase #7	$106.38	4.383%	$111.0426	$111.04	$111.05	$111.00
7 purchase totals =	$773.25		$830.7654	$830.77	$830.80	$830.70