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	$238.84	6.806%	$255.0955	$255.10	$255.10	$255.10
Purchase #2	$118.98	10.332%	$131.273	$131.27	$131.25	$131.30
Purchase #3	$36.94	13.635%	$41.9768	$41.98	$42.00	$42.00
Purchase #4	$240.84	7.477%	$258.8476	$258.85	$258.85	$258.80
Purchase #5	$45.67	13.253%	$51.7226	$51.72	$51.70	$51.70
Purchase #6	$151.61	9.841%	$166.5299	$166.53	$166.55	$166.50
Purchase #7	$165.52	9.459%	$181.1765	$181.18	$181.20	$181.20
7 purchase totals =	$998.40		$1,086.6219	$1,086.63	$1,086.65	$1,086.60