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	$161.82	12.190%	$181.5459	$181.55	$181.55	$181.50
Purchase #2	$110.60	12.746%	$124.6971	$124.70	$124.70	$124.70
Purchase #3	$48.32	12.661%	$54.4378	$54.44	$54.45	$54.40
Purchase #4	$77.64	10.301%	$85.6377	$85.64	$85.65	$85.60
Purchase #5	$180.36	4.232%	$187.9928	$187.99	$188.00	$188.00
Purchase #6	$144.52	11.332%	$160.897	$160.90	$160.90	$160.90
Purchase #7	$113.38	12.409%	$127.4493	$127.45	$127.45	$127.40
7 purchase totals =	$836.64		$922.6576	$922.67	$922.70	$922.50