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	$155.64	4.434%	$162.5411	$162.54	$162.55	$162.50
Purchase #2	$171.43	6.616%	$182.7718	$182.77	$182.75	$182.80
Purchase #3	$72.52	7.666%	$78.0794	$78.08	$78.10	$78.10
Purchase #4	$110.46	8.480%	$119.827	$119.83	$119.85	$119.80
Purchase #5	$84.78	5.708%	$89.6192	$89.62	$89.60	$89.60
Purchase #6	$18.78	12.520%	$21.1313	$21.13	$21.15	$21.10
Purchase #7	$234.31	7.853%	$252.7104	$252.71	$252.70	$252.70
7 purchase totals =	$847.92		$906.6802	$906.68	$906.70	$906.60