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	$65.80	9.280%	$71.9062	$71.91	$71.90	$71.90
Purchase #2	$175.65	6.564%	$187.1797	$187.18	$187.20	$187.20
Purchase #3	$165.92	12.841%	$187.2258	$187.23	$187.25	$187.20
Purchase #4	$78.90	5.856%	$83.5204	$83.52	$83.50	$83.50
Purchase #5	$196.57	12.808%	$221.7467	$221.75	$221.75	$221.70
Purchase #6	$78.68	13.632%	$89.4057	$89.41	$89.40	$89.40
Purchase #7	$38.57	4.492%	$40.3026	$40.30	$40.30	$40.30
7 purchase totals =	$800.09		$881.2871	$881.30	$881.30	$881.20