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	$148.94	6.654%	$158.8505	$158.85	$158.85	$158.90
Purchase #2	$95.36	8.402%	$103.3721	$103.37	$103.35	$103.40
Purchase #3	$162.95	11.605%	$181.8603	$181.86	$181.85	$181.90
Purchase #4	$138.67	8.541%	$150.5138	$150.51	$150.50	$150.50
Purchase #5	$87.49	7.702%	$94.2285	$94.23	$94.25	$94.20
Purchase #6	$41.48	10.630%	$45.8893	$45.89	$45.90	$45.90
Purchase #7	$178.30	3.151%	$183.9182	$183.92	$183.90	$183.90
7 purchase totals =	$853.19		$918.6327	$918.63	$918.60	$918.70