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	$128.70	7.377%	$138.1942	$138.19	$138.20	$138.20
Purchase #2	$27.46	13.410%	$31.1424	$31.14	$31.15	$31.10
Purchase #3	$135.33	7.379%	$145.316	$145.32	$145.30	$145.30
Purchase #4	$79.32	13.582%	$90.0932	$90.09	$90.10	$90.10
Purchase #5	$171.90	4.632%	$179.8624	$179.86	$179.85	$179.90
Purchase #6	$164.36	8.455%	$178.2566	$178.26	$178.25	$178.30
Purchase #7	$244.43	9.715%	$268.1764	$268.18	$268.20	$268.20
7 purchase totals =	$951.50		$1,031.0412	$1,031.04	$1,031.05	$1,031.10