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	$122.66	11.688%	$136.9965	$137.00	$137.00	$137.00
Purchase #2	$24.54	11.580%	$27.3817	$27.38	$27.40	$27.40
Purchase #3	$97.30	3.604%	$100.8067	$100.81	$100.80	$100.80
Purchase #4	$112.62	5.118%	$118.3839	$118.38	$118.40	$118.40
Purchase #5	$50.86	4.773%	$53.2875	$53.29	$53.30	$53.30
Purchase #6	$73.65	12.464%	$82.8297	$82.83	$82.85	$82.80
Purchase #7	$82.63	8.227%	$89.428	$89.43	$89.45	$89.40
7 purchase totals =	$564.26		$609.1140	$609.12	$609.20	$609.10