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	$235.40	8.345%	$255.0441	$255.04	$255.05	$255.00
Purchase #2	$54.77	13.608%	$62.2231	$62.22	$62.20	$62.20
Purchase #3	$140.31	12.675%	$158.0943	$158.09	$158.10	$158.10
Purchase #4	$224.33	11.230%	$249.5223	$249.52	$249.50	$249.50
Purchase #5	$31.97	5.141%	$33.6136	$33.61	$33.60	$33.60
Purchase #6	$181.39	9.549%	$198.7109	$198.71	$198.70	$198.70
Purchase #7	$137.69	9.270%	$150.4539	$150.45	$150.45	$150.50
7 purchase totals =	$1,005.86		$1,107.6622	$1,107.64	$1,107.60	$1,107.60