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	$181.26	13.201%	$205.1881	$205.19	$205.20	$205.20
Purchase #2	$92.61	11.684%	$103.4306	$103.43	$103.45	$103.40
Purchase #3	$39.85	3.833%	$41.3775	$41.38	$41.40	$41.40
Purchase #4	$247.56	7.232%	$265.4635	$265.46	$265.45	$265.50
Purchase #5	$38.72	4.719%	$40.5472	$40.55	$40.55	$40.50
Purchase #6	$116.74	12.395%	$131.2099	$131.21	$131.20	$131.20
Purchase #7	$103.59	7.117%	$110.9625	$110.96	$110.95	$111.00
7 purchase totals =	$820.33		$898.1793	$898.18	$898.20	$898.20