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	$72.90	7.667%	$78.4892	$78.49	$78.50	$78.50
Purchase #2	$54.29	13.488%	$61.6126	$61.61	$61.60	$61.60
Purchase #3	$128.62	7.615%	$138.4144	$138.41	$138.40	$138.40
Purchase #4	$185.52	4.206%	$193.323	$193.32	$193.30	$193.30
Purchase #5	$25.96	9.621%	$28.4576	$28.46	$28.45	$28.50
Purchase #6	$235.58	4.287%	$245.6793	$245.68	$245.70	$245.70
Purchase #7	$166.37	12.384%	$186.9733	$186.97	$186.95	$187.00
7 purchase totals =	$869.24		$932.9494	$932.94	$932.90	$933.00