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	$111.38	7.740%	$120.0008	$120.00	$120.00	$120.00
Purchase #2	$248.52	10.399%	$274.3636	$274.36	$274.35	$274.40
Purchase #3	$103.43	11.839%	$115.6751	$115.68	$115.70	$115.70
Purchase #4	$122.85	9.339%	$134.323	$134.32	$134.30	$134.30
Purchase #5	$158.68	9.620%	$173.945	$173.95	$173.95	$173.90
Purchase #6	$165.27	9.575%	$181.0946	$181.09	$181.10	$181.10
Purchase #7	$100.69	10.342%	$111.1034	$111.10	$111.10	$111.10
7 purchase totals =	$1,010.82		$1,110.5055	$1,110.50	$1,110.50	$1,110.50