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	$110.29	12.172%	$123.7145	$123.71	$123.70	$123.70
Purchase #2	$114.38	12.308%	$128.4579	$128.46	$128.45	$128.50
Purchase #3	$226.84	13.760%	$258.0532	$258.05	$258.05	$258.10
Purchase #4	$141.81	8.661%	$154.0922	$154.09	$154.10	$154.10
Purchase #5	$139.60	7.740%	$150.405	$150.41	$150.40	$150.40
Purchase #6	$231.38	7.384%	$248.4651	$248.47	$248.45	$248.50
Purchase #7	$139.75	3.735%	$144.9697	$144.97	$144.95	$145.00
7 purchase totals =	$1,104.05		$1,208.1576	$1,208.16	$1,208.10	$1,208.30